elements of practical geography

Elements of Practical

GEOGRAPHYR.L. Sing h

URana P B. Singh

ELEMENTS OF PRACTICAL GEOGRAPHY

o ^ a a a o 9 .B a f j^ Ofl *. 869125,5 0 l 4

ELEMENTSOF

PRACTICAL GEOGRAPHY(Fully Revised and Enlarged Edition)

R.L. SINGHPh. D. (London)

Ex-Professor & Head Department of Geography

Banaras Hindu University, Varanasi

RANA P.B. SINGHPh. D.

ReaderDepartment of Geography Banaras Hindu University, Varanasi

k a l y a n i p u b l i s h e r sNEW DELHI LUDHIANA

71S7'S8

KALYANI PUBLISHERSHead Office:

1/1, Rajinder Nagar, Ludhiana-141 008.

Branch Offices:4863/2B, Bharat Ram Road,24, Daryaganj, New E)elhi-110 002.B-16, Sector 8, NOIDA (U.P.)52, Shanti Complex, 26/2 Ranganathan Street,T. Nagar, Madras-600 017 Jhola Sahi, Cutuck (Orissa)3-5-1108, Narayanaguda, Hyderabad-500 029 No. 10/2B, Ramanath Mazumdar Street,Calcutta-700 009

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Catalouging Data

Singh, R,L. (1917) and Singh, Rana P.B. (1950) :Elements of Practical Geography. Fully Revised and Enlarged edition. 74 tables, 383 figures, 14 appendices, index, xii + 421 pp. January 1991. Kalyani Publishers, New Delhi.A text book covering overall aspects of Practical Geography at Bachelor and Master level courses and also in short giving direction for research procedures at higher level.

C opyright 2 6 th Jan u a r y , 1991. R.L. S ingh and R ana P.B. S ingh ^

Printed in 1992

Reprint 1997 ISBN 81-7096-441-5

P r in te d in In d ia a t Taj PressA -35/4 M aya Puri Indl. A rea Ph-I N ew Delhi 110 064

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PREFACE

ediuon published in 1951, authored by R r s i n g h and of the Rrstrev,s,on and new additions to the book wiUenfbTe L , ? knowledge of geographical science which n o ^ l l ^ o nh comprehend the growing and advancingwith humanities. Ih e new chapter on System technologythe students towards comprehending modem techniaue^^ l will awakentheir mapping and representation though s o D h S ic r^ - i i 7 Processing even complex data andurgent need for the balanced and integrated courses o f nh ? suggested there is analong with cybematics in view of th ^ d ev e lo L T f fand provide logicai criticism; m i th e m td f E c t l " : ! ? ' 7 ' ^ 'computer programming and cybematics wUihein in eeom nh , Ptocess; and fmally theand interpretation of spatial phenomena. Through s u c l ^ m S r computation, mappingm comprehending as weU as solving reai worfd situ^donranrt geographical knowledge

Another new chapter nertains w 'Ph , and problems will be made possibleexplanations to materials and equipment used P*'o Interpretation. Here pertinentphoto are grven. It may be remarked that the use of air phomfo ih' techniques for interpreting airdata rs rncreasr^ng day by day and the students of g e o if e n c ^ c l* nds of geographicalIn rh T n materials that have been provided in rtv- n r l 2 Pmcticai steps.la ctapter 7 as brought out by George F Jenks special I n W chapters may also be noted here,w u la u o n drstribution in an area have been ex a rn i;!^ ,^ c h l l P^cming ofsome of the methods are also briefly explained sncii T 2 4-' significance is explained andemp oyed rn geographical formulations. The important m e t h o d f r e q u e n t l y analysts and computerizauon are discussed in ^ technrques of model building syster^^^aucules drawn on different p ro je c ^ n s^ e e x p S l l e r l ^ T f field study of an area/region are explained for die benefit of P *' Pce

CONTENTS

Chapter 1m a p s

Topographical M apT W ^ls^MapZ Cadasiral Maps.Uses of Maps. Map Drawing Equipment D J">Ponance andPencls and Pens. Tints and P a t L T Colours,

pier 2 LLES

Graphic S M t 'co X u " ,;g p"^^ sion of Scales. Use of

Scales. Pace Scales. R evoluLn Scale? r p e d S Different Units. TimeSc^es. Scales of VerUcals. P e rsp e c h v rS c a llj D ia T c RootEttlargement or Reduction o f Sc^es L u a r l ? t^ L ?" Scales.Instrumental Method. Pantogtaoh E id n i u Triangle MethodMethods. Combining S c l ? ' 's c I f - d f h o t T ^ ^ Measurement of Distance. Measurement oT Am? S? la titude.Planimeter. ot Arcs . Square Method. Other Methods.

Chapter 3r e l i e f d e p i c t i o n

s h a ^ Valley. U-shaped Ceorge. W ate rfa irt^ C tffs. Fiord coast. Ria coast. Sand dunnes n " ' '^ = ors.mto Angle of Slope and vice versa. Finding S l o ^ ? l f ' - Conversion of Gradient! L long C m v e r L [ ? r ? o " a d ? ' '^ " ' -^ * >SS"'"Pon

*'b,hty. Interpoiation of Contour. Contour R epresenttfo?.'"'

Chapter 4

Profiles. Composite Prollles.Slot)eAnfr f lf' ^ P^nmposed Profiles. Projected

- .c r m tn a t to n o f D ,,O u tc r o p , comp,Chon

33-4S

49-82

(viii)

of a bed Unconformity. Overlap. Drift Deposits. Folds. Faults. Outliers and Inliers. Method of drawing Sections. Hints for drawing the Section. Description of the Map. Representation of igenous activity on Geological Maps. Form of Rock Outputs, Width of Rock Outputs. Structure of Drainage.

Chapter 5INTERPRETATION OF TOPOGRAPHICAL MAPS

Topographical Maps of India. Conventional Signs. Hints for the scientific study of Topographical Maps : Preliminary information. Observation of the Topography. Picturing the sheet as a whole. Observing the Relief, Observing the Drainage and its Pattern. Observing the Coastal Region. Vegetation. Observing Human Settlements. Observing Means of Communication and Irrigation Study of some Selected Sheets : Mirzapur and Adjoining Regions : Introduction. Physical Feature. The Vindhyan Plateau Vegetation. Settlements. Means of Communication. Means of Irrigation and water supply. Nature of Occupation. Dun Valley, Almora and Adjoining Region. Nainital and Adjoining Region. The Skardu and the Adjoining Region-Ranchi District. Hazaribagh District. Badland Topography of the Rewa State. Gorakhpur District. Plains of West Bengal. East Bengal Plains. Orissa Coastal Region. Masulipatam and the Adjoining Region in the Kistna District. East Godavari District. Mangalore Coastal Region in the South Kanara District.

83-118

Chapter 6W EATHER MAPS 119-160

Definition. The Observations : Pressure. Wind Direction. Wind Velocity. Deflection of Winds. Temperature. Humidity Visibility. Cloudiness. Cloudform. Rainfall. Weather Symbols. Beaufort Notation. Some Weather Phenomena Defined : Hail. Snow Sleet Frost. Rime. Mist and Haze. Squall. Line Squall. Corona and Halo. Aurora Borealis.Zodiacal Light. Mirage. Isobaric Systems. Depressions or Cyclones : Tropical Cyclones.Anticyclones. Secondary Depressions. Trough of Low Pressure. Indian Wedge. Col.Weather. Indian Weather Maps. Cold Weather SeasonA Wedge of High Pressure, A Trough of Low Pressure, Anticyclone over Peninsula, Cyclone over North India. Hot Weather Season, Season of General Rains. Season of the ReU'eating Monsoon. Reading a Weather Map. Some Notes on the Weather Maps of India. Metric Units for Weather Reports. Cyclonic StormsDepressionsThunder Storms. Examples I, Pressure, Wind,Sky Condition, Precipitation, Pressure Departure from Normal. Temperature Departure from Normal, Sea-condition. Example II, Pressure, Wind, Sky Condition, Precipitation,Departure of Pressure, Departure of Temperature, Sea Condition. Weather Forecasting.Summer Monsoon. Winter Monsoon. West European Weather : Cyclone or Depression.Anticyclone.

Chapter 7REPRESENTATION OF STATISTICAL DATA 161-200

Diagrams and Diagrammatic Maps. Methods of Drawing Diagrams : Bar or Pillar or Column. Blocks. Block Piling Method. Wheel Diagrams. Pictorial Diagrams.Star D iagram s. Im portance of Diagrams. Graphical Representation. Climo- graphs. Hythergraphs. Ergographs, Band Graphs, Compound Pyramids. Superimposed

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âm ids. Cartograms. Rectangular Cartograms. Traffic Flow Cartograms, Isochronic ^togram s. Distribution Maps. General Requirements for the Construction of

istribution Maps. Methods of Drawing Distribution MapsColour or Tint Method.Method, Isopleth Method, Shading or Choropleth Method,

S n e r^ ^ ^ Multiple Dot Method, Diagramatic Method. Population Maps. Some Clim M T Techniques for Population Mapping. Stock Maps. Crop Maps. Distnûtion^lVfeps"^'^^^^ Maps. Mineral Maps. Advantages and Limitations of

Chapter 8

S " o ? s L T t e c h n iq u e sReDresentafinnc nf n Types of Table. Frequency Distribution. GeographicalT e n te y DistribuUons. Histograms. Measures of Location or CentmlMedian Mode Group^ Data. Short Cut Method for Calculation of Mean,or Dispersion Rancrp Dispersion or Variability, Absolute Measures of viiationStandard Deviation R d ^ Deviation or Mean Deviation. Quartile Deviation.Two Scales IntemrPi r Measures of Dispersion. Comparative Assessment of theM oL g A v e ^ Series. TlteRegresfion. CoLlatin^ r Diagrams, Correlation and LinearCo-efficient Rank Gn i Grouped Data. Regression Lines. Regressioniô-etiicient. Rank Correlauon. Test of Significance.

Chapter 9

SYSTEM ANALYSIS, MODEL BUILDING AND COMPUTERIZATIONLinear Sicuation, Spacing

of Con T . cn Measures. Matrix and Graph ConnecUvity. DegreeTowarHTvf^rti r- Set TheoreUc ApproachMaif' Pr H Model. Potential Surfaces. Computerization ProgramMîng. Pi-ocedures. Input Description. AddiUonal Assigned Names. Piogiams Analysis Data. Input Lisung. Program. Conclusion. ^

Chapter 10m a p p r o j e c t i o n

Meaning and Use. M ef Historical Aspect. Classification of Map Projections The Consriucuon of Map ftojecuons. Simple Conical Projection with One Standard Parallel I t T*o Standard Parallels. Bonnes C o n i c r S o nPolyranic j ponical Equal Area Projection with One Standard Parallel ^ Pofar 7 Projection with One Standard Parallel. Zenithal ProjecUonStereographic Po ar Zenithal Projection. Gnomonic Polar Zenithal P r S o ^^ 'S '^ i d i s t a r i t S ;S Û o? .e"' Zenithal Equal Area Projection. Polar^Hndrical Projection. Simple Normal Zenithal Projection. NaturalMercators Projection, Sinusnirt i Cylindrical Equal Area Projection.Projection. Galls Projection ^ Projection. MollweidsChoice of Projections. SummaH S' r Inêmauonal Map Projection,graticules drawn on different Solution of Errors in thescales for gratitudes drawn on Man Pm- Jf.^^*"^~Methods of constructing comparative

P r'rojccuon. Methods of constructing comparative scales.

201-225

226-251

252-309

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Chapter 11SURVEYING 310-343

Field Notes, Chain Surveying, Importance of Chaining. AppliancesChains, Taps,Offset Staff, Ranging Rods, Arrows Optical Square, Magnetic Compass. Procedure.Errors, Obstacles to Chaining. Plane-Table Surveying. Equipments, Procedure for a Comple the Survey. Suggestions. Sources of Errors. The Three Point ProblemMechanical Method, Graphic Method, Trail Method. Advantages and Disadvantages of Plane Table Surveying. Company Surveying. The Prismatic Compass. Procedure Suggestions for accurate work. Plotting. Closing Error. Detection and Elimination of Local Attraction. Sources of Errors. Advantages and Disadvantages of Compass Surveying. Disadvantages of Traverse Surveying. Methods of Traversing By Chain or Tape. By Prismatic Compass, By Plane Table, By Theodolite. Adjustment of Errors in O ^ n Traverse. Contouring. Spirit Level. Plotting. Closing Error. Detection and Elimination of Attraction. Sources of Errors. Advantages and Disadvantages of Compass Surveying, Parts of a Transit Theodolite. Procedure. Plotting. Co-oridinate Method of Traverse Computation, Calculations. Traverse Surveying. Methods of Traversing.Adjustment of Errors in Open Traverse. Contouring. The Spirit Level. Practical Contouring Sextants, Nautical Sextant. Procedure. Basis of Large Scale Maps.Triangulation.

Chapter 12PH OTOG RAM M ETRY AND AIR PH OTO IN TERPRETA TION 344-357

Some defined terms associated with aerial Photographs and aerial Photographic Surveys.General equipment used in air photo interpretation. Parallax bar or Stereomicrometer.Aerial or Radial-Triangulation and Preparation of Miner Central Plot or Grid. Aerial Mosaic. Interpretation of Aerial Photographs. To find the number of air photos. List of conventional symbols. Dip and Strike.

Chapter 13M INERALS AND ROCKS 358-375

Minerals, Characters depending upon Cohesion and Elasticity : Form, Hardness, Fracture,Cleavage, Characters depending upon Light, Specific Gravity of the Mineral, Other Minor Characters, Classification; Rock Forming Minerals. Ore Forming Minerals,Description of Minerals. Soft Minerals. Medium Soft Minerals. Medium Hard Minerals.Hard Minerals. Very Hard Minerals. Light Minerals. Medium Light Minerals. Medium Heavy Minerals. Heavy Minerals. Very Heavy Minerals. Metallic and Non-metallic Colours. Rocks Igneous Rocks. Igneous Granite. Pagmatile. Syenite, Diorite. Gabbro.Pcriodolite. Dolerite. Basalt. Rhyolile. Pumice. Sedimentary Rocks. Sandstones. Shales.Lime stones. Breccia. Conglomenalc. Metamorphic. Quariize. Slates.

Chapter 14FIELD STUDIES & RESEARCH STEPS 376-393

Training the student in Field Geography. Instructions for the Study of a Typical Area.Giridih and Adjoining Region. Arrangement and Equipment. Arrangement for Camping some Specific Areas. Mirzapur and the i^ jo in ing Region. Measure the Depth of Water Table or Sub-Soil Water. Kodarma Parasnath-Jharia-Region. Jabalpur and the Adjoining Region. Setting of Map in the Field. Collection of Data in the Field. Taking the Soil Sample, Measuring the Depth of Water or Sub-soil Water. Collecting of Data regarding Social Geography. How to write the Regional Account. Problems and Patterns of field- research. Five steps of research, lime-budget. Village Report : An OuUine.

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^ P E N D IC E S , 394.421lA. Use of Logarithms, 394IB Use of Units of Measurement and Conversion Tables, 395-3962. ^ (Chi-square) Table, 3973. Z value Table, 3984. t distribution Table, 3995. Logarithms, 4(X)-4016. Antilogarithms, 402-4037. Angles, degrees and values, 404-4058. Square roots (1 100), 406-4099. Cube roots (1_1000), 41041510. Reciprocals (1 10), 416-41711. Random sampling numbers, 41812. Pesudo-random numbers, 41913. Tailed t test values, 42014. F distribution value, 421

Z

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Chapter 1

MAPS

1. Meaning and DefinitionThe map may be defined as the rejM-esentation

of the earths pattern as a whole or a part of it, or of the heavens cxi a plane surface, with conventional signs, drawn to a scale and projection so that each and every point on it corresponds to the actual torestrial or celestial position. By gradual evolution in the science of map-making it is now possible to picture the earths pattern more precisely and also to compress varied types of necessary information in a single map sheet without any verbose description. The amount of information to be represented on the map depends on : (0 Scale, (ii) Projection, (Hi) Conventional signs, (iv) Skill o f the draughtsman, and (v) Methods o f map-making. A large scale makes for a big size of the map which can conveniently and legibly depict features of the area in much detail. The ffainework of the map is based on the way how the graticule, i.e the longitudinal and latitudinal network is prepared. This depends on the posiUon of the area on the earths surface and also on the type of the map. The perfection of conventional signs has made it possible to compress maximum of information in the minimum of space without losing legibility. Every symbol, sign and letter which has been adopted for representing topographic forms conveys a definite meaning; so the map becomes a kind of code which cannot be fully interpreted without a complete knowledge of the conventional signs. The draughtsman, by his unique skill and technique, may give a lively touch to his drawing, which, otherwise, becomes less attractive.

There are various ways by which the earth is mapped : (I) by actual survey with the help of the mstruments like chain, planetable, prismatic compass and theodolite, etc., (II) by photographs and (III) by

freehand sketches and diagrams. (IV) Now, by computer maps are being precisely constructed. Satellites and remote sensing are also being used for mapping large areas of the earth quite acciuately. The method of mapping depends on the size of the area, on the degree of accuracy aimed at and on the amount of detaUs required. On a topographical survey map every point on the map bears a true relationship with the corresponding point on the ground. Photographs are, no doubt, true_ representatives of the earth s designs but they are pictorial in appearance and can show only a very small portion at a time. Landstat data and remote sensing images are available to prepare the most accurate and detailed maps for any region. In sketch-maps and diagrams the scale is less accurate.

2. History of MapsMaps are not the invention of the modem age.

They were in existence even in olden times. But the earliest maps were, in general, highly pictorial presenung the ideas by a rough sketch or picture, without any scale or accuracy regarding relative position or size. For the first time, over 3000 years ago, the Egj^tians prepared more feasible maps, showing particularly land boundaries with a view to making proper assessment of revenue. The few Egyptian maps which still survive are of little interest from the cartographic point of view as they represent only small areas of surface and are rather rough sketches. *

The credit for laying the foundaUon of modem cartography goes, in fact, to the ancient Greek geographers whose achievements in this field were not excelled till the 16th century. The recognition of the earth as a spheroid with its poles, equator and

"7"


tropics, the division of the earth into cUmatic zones, the development of the system of graticules and the formulation o f the first projections, and the calculation of the size of the earth are all achievements of Greek geographers like Aristotle, Eratosthenes and Ptolemy etc. The Greek cartography

culm inated in the works of Ptolemy. His Geographia contained a map of the world and other

twenty-six detailed maps. On his world map Asia and Europe extended over 180 though they actually cover only about 130. Likewise, the length of the Mediterranean has shown as 62, which is really 42

180

O90

Fig. 1. Showing Ptolemys world.

only (vide Fig. 1). Considering the limitations of travel in those days, Ptolemys maps, however crude and rough they may seem to appear, should be appreciated. His Geographia disappeared for some time and as such there was a steady decline in the art of map-making. The work of the Romans alone was available which provided a very inferior source to the succeeding geographers. Unlike the Greeks, the Romans paid little attention to mathematical geography. They adopted the old disk maps of the early map-makers which suited military and administrative purposes only. The Pentinger Table, an example of Roman cartography, is a Graphic compendium o f mileages and military posts throughout the empire. During the middle ages maps were produced in a fairly large numberover 600, discovered so far, but they simply represent the Roman disk type. The Arab geographers followed the Greek methods and made some improvements ih the maps and showed, at least, the Islamic world ccHTectly.

The recovery of Ptolemys Geographia in the 15th century, the invention of printing and engraving, and the age of discoveries, all these exerted a great force in ushering in the renaissance o f map-making. The Italians, Spaniards, Portuguese, the Germans and the Dutch with their successive efforts perfected the art of drawing maps to such an extent that map- publishing became a very lucrative business in the 16th century. Map printing presses of Venice and Amsterdam which gave employment to many workers, could be started due to the invention of printing and engraving. But on the whole the sixteenth century maps reproduced P tolem ys distortion in the shape and distance. Mercator, who liberated cartography from the influence of Ptolemy, on his may of Europe published in 1554, reduced the length of the Mediterranean to 53. It was not until the close of the 17th century than its actual length of 42 was shown on the map of Delisle.

With the perfection of triangulation survey and measurement of longitude by chronometer, the

X

MAPS

reformation in cartography was introduced by the French in the beginning of the 18th century. In the latter half of the 18th century when England became the forem ost m aritim e power in Europe, a cartographic centre was developed in London. It was during this period that the military operations necessitated the preparation of detailed and accurate topographic m ^ s under the auspices of the army. The first national survey was conducted in France by C.F. Cassini whose work was continued by his wn, and was completed during the Revolution. Thus Carte Geometrique de La France was completed on a 1 : 86,400 scale in 1789. Napoleon, a great supporter of survey and mapping, started a number of surveys in Italy, Germany and Egypt England followed the lines of France and the Ordnance Survey was instituted in 1791. The first sheet on the scale of one inch to the mile, of Kent and southern Essex was published in January, 1801. Then other National Surveys were organised in Spain, Germany and Switzerland, etc.

In the foUowing two centuries great advances were made in science and education. The development of lithography, wax-engraving and photo-engraving in combination with colour printing d i ^ g 1804-60, gave much stimulus to map-drawing. Rich and colourful symbols were used in place of black-and-white technique of older maps. Germany, France and England produced a number of maps and atlases. The Stieler Atlas of Germany, French atlases of Vidal de La Blache and Vivien de St. M artin and English atlases o f Philips and Bartholomew, etc., may be noted. New types of National atlases,* giving all available information about one nation, were produced in France, U.S.A., ^^d U.S.S.R. The French Colonial Atlas and the American Atlas of Agriculture owe their caigin to

the ^rfection of the new technique. The introduction of airplane photography in the beginning of the 20th century ushered in a new phase in topographical surveying. This method is quicker, cheaper and especially useful for mapping comparatively

unknown or unexplored regions. All advanced countries of the worldU.K., U.S.A., and U.S.S.R. etc., have made extensive use of the airplane photographic survey.

Recently the U.S.A. has collected through Satellite^LANDSTAT1 various kinds of images and pictures during two years period (July 23,1972 July 23, 1974) which have been processed by computerized cartographic tools to produce the world map into 7 parts (WP.S. 17). To make these maps easily understandable meaningful system of shading and colour scheme have been employed. Consequently, full analysis of topographical and landform maps in a scientific way can be made.

air surveying operations were started in India in 1924 but litde could be done till 1928 when with the accumulated experiences gained in Malaya, Borneo and Burma, a map of the Chittagong district was prepared on the 16 inches to the mile scale. Dunng the following years four districts of Bengal, nearly 4,000 sq. miles in U.P. and one thousand square miles of land in Baluchistan, for oil prospecting, were surveyed from the air. RecenUy aenal photographs for some specific areas like Damodar valley have also been prepared but these are not yet available for public use. So far about three lakh square miles of area have been surveyed. But in view of the necessity of prospecting for mineral resources, planning of public works, improvement of towns, preparation of large scale land utilization maps and prevention of floods and soil erosion, etc., we are badly in need of geographical information. It is high time that our nauonal govemment should organise extensive air surveys for making detailed maps which will render a great service in national planning.

3. Types of MapsMaps are usually drawn of show different details

on a large or small scale. The details that are to be shown on it may be so varied that even if the scale be fairly large, their representation on one map may

RecenUy an Irrigation Adas of India has been p ub lish A O Phy^ographic maps of India have also been out

elements of practical geography

lead to confusion and ambiguity. Hence it is customary to show different details in separate maps. Though certain features of the area may have marked correlation with others, yet, to avoid confusion, separate maps are drawn for each on the same scale and their causal relationship may be studied by comparing one with the other. For instance, rainfall and vegetation maps of a country drawn on the same scale may be easily correlated. In a large scale map more detailed features may be usefully shown as compared to small scale maps. In topographical maps prepared on one inch scale, for example, both natural as well as cultural features are marked with clarity, whereas in atlases, the physical and economic maps ^ separately drawn so that they may be properly interpreted.

It is, therefore, essential to pay more regard to two things while classifying maps into different categories ; (1) Scale and (2) Purpose or content. According to scale maps may be classified as follows:

1. (a) Cadastral: The term cadastral is derived from the French word cadestre meaning register of territorial property. The cadastral maps are drawn to register the ownership of landed property by demarcating the boundaries of fields and buildings etc. They are especially prepared by the government to realize revt lue and tax. The village maps of our country may be cited as example, which are drawn oil a very large scale, varying from 16 inches to the mile to 32 inches to the mile so as to fill in all possible details.

The city plan maps may also be included in this category. The British Ordnance Series prepared on 1 : 2400 or 25 inch scale and 6 inch scale, 12 inch scale may also be included in this type.

{b) Topographical maps : The topographical maps are also prepared on a fairly large scale being based on precise surveys. They show general surface features in detail comprising both natural landscape and cultural landscape. Unlike cadastral maps, the scale of topographical maps varies in general from one inch to the mile to 1/4 inch to the mile. They do not show boundaries of individual plots or buildings; it is rather the principal topographic forms like relief and drainage, swamps and forests, villages and towns

and means of communication, etc., that are depicted on them. It is for this reason that for geographCTS these are the most valuable tools. As already noted in precedmg paragraphs, these maps were drawn after the perfection of the methods of triangulation survey. Modem airplane photogr^hs may be regarded as new but good additions to this type. A vertical airplane i^otograph is more effective when its scale be over 1 : 20,000. These photographs have a particular value in so far as they clearly exhibit many relationships by providing a complete view of several different maps.

The topographical maps of different countries, however, do not show unifcMmity. They differ both in scale and scheme. The most standard and popular topographical survey maps of British Ordnance Survey are one inch m ^ s . Most of the urc^)ean sheets are on the scale 1: 25,000 to 1 : 100,000. In the U.S.A. the topo-sheets in general are drawn on 1 : 62,500 and 125,000 scale. India has followed, more or less the British scales. Recently metric system has been introduced in the country and as such one inch maps are now being revised to 1 :50,000 scale; considerable progress has been made in this direction.

The one-in-a-million (1" = 15.78 miles) map may also be included in this group which is designed to produce a uniform map of the world in various sheets of uniform size, shape and style. The one-in- a million map is also known as International map and the proposal for its acceptance as such was made by Prof. Penk at the Intemational Geographical Congress held at Berne in 1891. But an agreement between various nations was reached only in the London Congress held in November, 1909, when a specific scheme was prepared which was again supplemented and confumed in the Paris Conference in 1913. The Intemational map projection, a modified polyconic projection was devised for the drawing. When completed, the whole set will consist of 2,222 sheets, in the following way ; (i) Between 60 North and South latitudes there will be 1,800 sheets each covering 4 of latitudes and 6 of longitudes; (//) from 60 to 88 latitude both North and South of equator each sheet would extend ovct 4 of latitudes and 12 of longitudes, and thus, that total number of

X

MAPS

Sheets would be 420; (/) and there would be two circular maps for the polar areas, with 2" of radius India and U.K. have taken the lead in producing these maps.

. Walls maps are generally drawn^ Id ly so that they may be used in the class-room The world as a whole or in hemispheres is distincUy represented on the w dl maps. Wall maps may also be prepared fw a continent ot country, large or small, according to need. Their scale is smaller than that of topographical maps but larger than that of atlas maps.

(d) Chorographical or Atlas maps : The Atlas maps are drawn on a very smaU scale and give a rnore or less highly generalised picture regarding the physical, climatic and economic conditions of d ifferent regions of the earth. M ost of the topographical maps have been shown in colours to form atlas maps on which, due to the limitations of space, only main ranges of hills with impcMtant peaks important rivers, chief towns and main lines of ^ Iw ay s can be represented. Only a few atlases have ^ n prepared on a 1: 1,000,000 scale like the Times Survey Atlas o f the World. Little effort has so far been made in Iridia towards the compilation of school atlas maps, while, on the other hand, countries like Fiances, U.S.S.R. and U.S.A. have produced national atlases. S.P. Chatterjees Bengal in Maps has given stimulus for the publication of such atlases as Bihar in Maps. State atlases have also been completed by various institutes, such as the Atlas o f Mysore by the Indian Statistical Institute; and Planning Atlas ofUJ* by G .BP. Institute (1988). The Registrar General has thought out Census atlases of India, and also for each state (1989-90).

2. The other classification is based upon the purpose or the content of the map. The pattern of the earth is consequent upon both natural forces and human forces. So both natural features and manmade features evolved over different areas should be shown on maps. A map showing heavenly features is known as astronomical map. The map depicting surface forms is termed orographic or relief map. m s mdicates the bulges and depressions found over the surface. The level of land, its slope and drainage which IS represented by rivers and lakes are well marked on it. Sometimes clay models too are

prepared to show the relief of the land, which bring home the real picture of the surface. Recently aero- relief maps on plastic surfaces in appropriate colours have been brought out which are washable and can be conveniently used for teaching purposes. The rocks that from the crust of the earth, and their mode of occurrence and disposition are marked on Geological maps. A correlation of these m ^ s with the corresponding relief maps reveals the causes and evolution of landforms. Then there are weather and climatic maps. The weather map denotes the average condiuon of tem perature, pressure, wind and precipitation over a short period, which may range from a day to a season. Maps showing daily weather conditions are termed daily weather maps, while those showing the average of monthly or seasonal weather for winter or summer etc., are called winter or sunyner maps, etc. When averages of weather conditions over a long period say, over 10 years or more, are charted out on maps, they are defined as climatic maps. The maps showing natural flora are called vegetation maps. The soil map of an area exhibits various types of Mils covering the area.

On the other hand cultural patterns designed over the surface of the earth are also represented on the map; such maps may be termed ^'cultural maps". The occupancy of the surface of the earth by man has resulted in carving our various designs over it. On sm dl scale maps, in particular, it is not possible to depict all manmade features without losing legbility . So different types of maps showing different features consequent upon the activities of man, have been evolved. A political map shows boundanes between different states or boundaries between different political units within a country. Various spheres of influence of nations may also be expressed on political maps. Military maps record strategic points, routes and battle plans etc. Past events are symbolised on historical maps. Social organismstribes and races, their language, religion, etc.are also depicted on maps which may be called social maps. Maps exhibiting the nature and character of l^d-use may be termed land utilization maps which have been recently devised in U.K., U.S.A. China. Japan and other countries. Moreover we are not urifemiliar with pictorial and diagrammatic maps m which, at the cost of precision and true proportion great attention is paid towards illustrating the fects


in such a manner as to make them more impressive and appealing to the mind. On such maps some facts are charted out and represented by graphs and cartograms.

The map is, however, named after its content when only one aspect or feature is shown. For example, if only means of communicationroads, railways, airways, etc.,are shown it may be called communication map. A population map denotes distribution of man over an area. When many features are shown on a map, it may be named either after the main idea reflected by it or according to the total aspect shown by iL For instance, the map showing Ae distributipn of important agricultural, mineral and industrial products, with imjwrtant centres linked by various means of communication may be termed economic map because from it the nature of econom ic developm ent of the region may be interpreted.

Maps displaying the distribution of different objects of definite value may be grouped under the head the Distribution maps. These present one characteristic feature of a certain area, even ignoring the exact location of the object if necessary. The item may be natural, like temperature, pressure, rainfall, flora and fauna, or, it may be cultural, showing agricultural and industrial products, etc. It may be contrasted w ith location m aps or physiographic maps in which the features marked on the map exactly correspond with those on the earth-surface. The distribution maps may be further sub-divided according to the method of construction. The data may be presented by : (i) colour, (ii) symbol, {iii) regular lines, (zv) dots, (v) shading, (vz)bars, (viY) block, (vm) circles, and (ix) spheres.

When different objects are shown by various colours the map is known as chorochromatic. The representation of density of population, fwest types, amount and intensity of rainfall, etc., may be done by different colours or different shades of one colour. In a map showing the distribution of crops cotton may be shown by C, wheat by W, maize by M and rice by R. Likewise, the distribution of coal may be shown by C, iron by F and gold by G, etc. Such maps may be termed Choro-schematic. Statistical data may also be shown by lines of equal value. Thus regular lines may be drawn on a m ^ to show equal amount of rainfall, temperature and pressure, etc. These lines are called isohyets, (isopluves), isotherms and isobars, etc., respectively. All those maps in which lines of equal values are shown are called isopleth maps. The distribution of sheep ot horse or any other object may be shown by putting dots of uniform size, each dot representing a definite number or quantity; these are called dot maps. Similarly, different shading by htxizontal, vertical and slanting lines or in check frnns may be adopted to show different density of population, location factor for industries, forest types, etc., such maps may be termed choropleth maps.* Bars, blocks, circles, spheres and other forms of representation are also included in cartogr^hic and diagrammatic representation of geographical data. The relative importance and technique of different types of distribution maps will be discussed in a subsequent chapter.

Thus, we may distinguish the following major groups of maps according to their purpose and con ten t:

Maps

Physicalor

Natural1

ICultural

I

I Distribution Economic Political MiUtary Historical Social Land Utilization Special

I ^ ^ ^ ^ n I-------------^ ^Astro- Orogra- Geological Climatic Natural SoU Charts Diagrams Cartograms Perceptual/

nomical phical Vegetation CogiStivT

*The choropleth m^s may represent all quantiflcation areal maps prepared on a basis of average numbers per unit area.

\

4. Importance and Uses of MapsMaps are the tools of Geographers. No other

science is so much dependent upon maps as geography though all use maps and diagrams to iUustrate their facts and data. As all sciences are directly or indirectly connected with the science of the earth, all types of maps may be regarded g e o ^ h i c in one sense or the other. Our planet is w big and presents such a variety of scenery that it is yery difficult for any individual to have personal observation of things all the world over. Not unlike books, maps are also records of various facts regarding the earth; but they are something more in that they make a direct a p p ^ to the mind and even the unknown and unseen lands may be unfolded in their original form. In a certain sense they are pictorial and as such a glance at them is more pleasant and easily brings home even a set of complex facts in their proper relationship. For example, a population map with towns of various sizes not only acquaints us with factual data regarding the distribution of man in rural and urban areas, but it explains .their causal relationship also. They at once jTCsent a concrete idea about other parts and peoples. Good maps furnish us with a wealth of information in its true perspective and so they are as good as pages of descriptions. With the help of topogr^hical maps regicxial geography of a country may be systematically described. It is with the help of maps and diagrams that many complicated landforms may be explained in a simplified manner. Thus, for academic purposes maps are very essential.

But for personal observation, maps are true p id e s not only to geographers but to other individuals too. They are useful to travellers and tourists in that they may guide them to their destination without their being under the necessity of enquiring about it from other local persons. It is needless to mention the importance of navigational charts for sea or air use. In military operations the services of mapstopographical maps or topo sheets in shortcan hardly be exaggerated. In unmapped areas advances are not free from risks and dangers. During opaations, maps render much help by indicating various routes and possible enemy positions. This is why the public use of the

topographical maps is restricted during war. Businessmen, industrialists and managers of factcaies and workshops also need maps and charts. The manager of a cotton mill by casting a glance over the production graphs, may at once understand whether his production is falling or rising and take further action, without incurring the trouble of going over a long list of daily production data. The government badly need maps for administrative purposes. Besides, maps are useful for planning and COTservation of natural resources of a country.

In conclusion, it may be noted that while the map is a guide and help to individuals in general and the government in particular; it is a shorthand script of geographers, which cannot be thoroughly followed without proper training and practice.

5. Map DrawingThe map is the traditional medium of the

geographer, and map drawing is now a well recognised discipline in which proficiency cannot be achieved without (z) manual skill and dexterity, () mechanical aids, and (Hi) critical knowledge of cartographic techniques and principles. All these require a systematic training which a student of geography is expected to undergo as an essential part of practical work. Maps, drawn in course of training, may be grouped into two classes : (a) compilation, and (b) originals. Sotic universities in India provide a systematic training in map drawings.

Then maps and illustrations ai^jearing in text books form a separate group. Map drawing for printing presents a somewhat different aspect from that for training purposes, and perhaps this fact seems to have been ignored by the authors and publishers.It may be suggested that while imparting training in map drawing, due emphasis should be laid on their printing aspects also.

Drawing EquipmentThough maps are drawn by human hands,

modern advances in drawing tools and matials have resulted in reducing the time spent on map drawing and standarding the total aspect of maps. Thus the famUiarity with not only the use of instruments but also with different types of materials and their

8elements of practical geography

qualities is a prerequisite for drawing a standard map. Essential drawing tools a re : (0 Drawing instrument sets containing dividers, compasses both ink and pencil, protractors, ruling pens; (ii) T-squares and triangles and celluloid set squares; (iii) Graduated scales and sliding rules; (iv) Drawing board and Table; (v) U. N. O. Stencils or Le Roy pens, particularly fcx- lettering; (vi) Drawing materials include paper, pencil, eraser, ink, colour, brush, reproduction whites, sticking tape, etc.

Drawing Table: A map makers table is different from other tables. It should have a hard surface of thick glass tilted at a slight angle with provision of illumination from below by a tubular light. For o r d i i ^ uses an adjustible drawing board made of one inch thick plywood may form the top of the table. The drawing paper may be stuck down by strips of Scotch or a^esive tape over each comer. A short T-square is used on the front of the table. In an attached tray the instruments few immediate use may be kept.

Papers: For drawing maps and other illustrations generally four types of papers are used: (/) drawing paper, {ii) tracing paper, (zu) plastic media, and (/v) graph papers. Each type varies in quality and has its specific uses and advantages and disadvantages. Smooth surfaced Saunders or Kent paper is a fairly good drawing paper for all finished map work. Cheaper media will neither stand erasure nor will they permit smooth colour washes or shadings. Transparent tracing papers are used for copying, and for tissue overlays that indicate various colours and tints. A good tracing paper is tough, and of a smooth mat surface with no gloss; maps for block making can be drawn directly on it in black profile ink. Any alterations and obliterations in the drawing can be made more easily on this papw than on Bristal can! Tracing papo^ will, however, expand easily on humid days; and especially for two-colour blocks it becomes difficult to bring about precise registration while reproducing the drawing. A change of 40 per cent in relative humidity may introduce about 2% distortion in either direction. Furtho-, these pq)ers tear easily, and it becomes essential to protect their edges by a kind of adhesive tape; for binding

the edges a small machine may be used.Tracing cloth is excellent for thick line work

and manuscript maps and for blue prints. But it is rarely used for fine map work.

Vellums are semi-transparent papers imprograted with oil which prevents distortion with changes in humidity. It is used for colour maps, but it is not easy to draw on vellum.

Cellophane, Tracilin, etc., are perfectly transparent and are very helpful in tracing details from airplane photography. Cellophane is dso used for protecting finished drawings.

Different kinds of plastic materials are now available for cartographical works. Celluloid sheets, both transparent and opaque take very fine lines both in pencil and in ink. They are washable also. Kodatrace, a grainless celloluse plastic material with finished malt on one side and tinted faint blue, allows over 74 pw cent light transmission; it is tough and flexible and can be cleansed easily.

Arithmetic graph papers ruled in inches or centimetres are used for drawing a wide range of graphs. Semi-logarithmic graph papers are required for frequency graphs. Circular graph paper may prove helpful in drawing some projections, wind roses etc. Percentage circular graph paper is helpful in accurate and quick plotting of divided circles. Triangular graph paper is used in plotting the variables, say of climate. Isometric graph paper facilitates the depiction of three dimensional figures, such as block diagrams. Fw plotting p'obability curves, say, of rainfall, etc., the arithmetic graph paper is very useful.

Inks and Colours: The standard ink used in drawing is called Indian ink which consists of find lamp-black suspended in a liquid medium. It is available in a number of brands and colours. Most brands are water proof and when it is deep black it photographs well. But it dries up very rapidly, so that the cartographer, particularly in fine map-work, must keep his line-work moving fast When exposed to air the ink in a bottle gets coagulated and unless it is corked well when not in use it soon deteriaates. The ink is also sold in the form of small sticks or cakes from which the ink is rubbed in a cup in

X

MAPS

required quantity. It is also supplied in plastic tubes from which the desired amount of ink of correct fluidity may be squeezed out

Unnecessary ink lines can be removed by W y in g reproduction white with a fine sable brush. They may be scratched with a razor blade or erased with an ink eraser.

Sometimes for clarity ordinary water colours made in tubes and cakes, or aniline powder-dyes are used in drawings. The use of crayons and coloured pencils results in cruder forms.

Much of the prehminary workIS done m pencil. To avoid rolling or slipping the hexagonal pencil is preferred to a circular one A good pencil writes even and dark line; it neither w e^s down too rapidly nor breaks easily. They are made m vanous grades of hardness: 8 H or 9 H pencU are hardest and will scratch or cut the surface of the paper; while HB pencils are of medium hardness and 6 B pencils are the softest.

^ variety of pens is available for drafting drffwent kinds of lines and for lettering purposes:

Gillott NOS.290 (soft). 291 (hard). 303 and 404. (ii) One or two double-pointed nibs (e.g. road pens) are used for drawing parallel lines, (m) A ball-pointed nib is used for dotung and suppling, (/v) Quill-type pens are of large vanety and make uniform lines; some ^ used for rivers that vary in width; for speedy ^ ttenng the quill pens are very advantageous, (v) The stub pen is lik*e a quill except that the tip-ends are flat and not tapering to a point; the width of the

lines drawn by this varies with its vertical and horizontal movements. For freehand lettering it is certainly a good pen. (vi) The BarchPayrant pen, though designed for lettering, is used by geographers more frequently for making uniform dots in distribution maps. The flow of ink is adjustable, a quality which makes it desirable for dotting process. (vii) The UNO pens of varying thickness are quite versatile and are used for drawing lines of uniform thickness and with stencils for lettering purposes. A certain amount of care is essential to maintain even flow of ink; it must be kept absolutely clean, (viif) The Le Roy pen (Fig. 2.) was originally designed for lettering but it has been found quite useful for other purposes also, (ix) The Pelican Graphers drawmg ink fountainpens are extremely versatile type for cartographic use.

Tints and Patterns: A very essential part of many maps is the shading or pattering that is done to differentiate one from another. This is commonly awomplished by drawing them laboriously by hand. Now patterns printed on transparent film ar available which can be easily used; zip-a-tone is the trade name of the best known material of this kind. More ^ n 150 patterns are available in different colours. The material is placed over the area and cut to fit into It. This is. however, not well known so far to our cartographers.

Some tints are set by the block-makers by mwhanical devices but the process of setting tints is relauvely more cosUy and also only a limited number of unts may be had by this process

p s .Tv . > ; ^ ir't>l i uViLij

Rg.2

Chapter 2

SCALES

DefinitionThe distances on the map are smaller than the

corresponding distances on actual ground. But the map always bears a definite proportion to the mapped area. The scale indicates the proportion which a distance between two points on a map bears to the distance between the corresponding points on the actual ground. If for instance, an actual distance of 5 miles is represented on the map by a distance of 1 inch, the scale is 1" = 5 miles.

According to our need we can have ''small scales and "large scales . The scale we choose primarily depends on (1) the size of area to be mapped, (2) the amount of details to be shown, and (3) the size of the paper. "Small scales show miles to the inch; as, for instance, the cycling and motoring maps which are generally either 1 mile to the inch or 2 miles to the inch. The atlas maps are drawn on a still smaller scale. These may vary from a few miles to the inch to several hundred miles to the inch. "Large scales are scales of inches to the mile. Navigators charts and property survey plans, for example, are drawn on large scales of say 6" to 1 mile, or 25" to 1 mile or even larger.

RepresentationThere are three ways in which the scale is

depicted on the map.1. By such a statement as 3 inches to the mile

or 1/3 mile to the inch.We are familiar with inch distances and, thus,

can easily read off miles on the map.2. By a graphic scale as shown in Fig. 4.Here a straight line is divided into a number of

equal parts and is marked to show what these divisions represent on actual ground.

3. By a Representative Fraction.This expresses the proportion of the scale by a

fraction in which the numerator is one and the denominator also in the same unit of length. For example, if the Representative Fraction (Commonly written as R.F.) is stated to be 1/100,(XX), or 1 :100,000, this means that one unit on the map represents 100,0(X) of the same unit on the ground. This unit may be an inch or a centimetre or any other foreign unit. If it is an inch, then 1" on the map represents 100,(XX)" on the ground, i.e., about 1.58 miles. If it is a centimetre, then 1 cm on the map represents 1(X),0(X) cm on the ground, i.e., 1 cm represents 1 kilometre. The advantage of expressing the scale in terms of the R. F. is that one can judge distances on a foreign map even if he is not familiar with the linear measurements of that country. For instance, if on a Russian map it is stated that one Paletz = one verst, then to a person who is not fam iliar w ith the R ussian system o f linear measurement it will carry no meaning. But if the same scale is expressed in terms of R P . it becomes 1 : 84,(XX) .-. 1 verst is equal to 84,(XX) Paletz. Obviously to one who uses an inch as the unit it will be 1"= 84,(XX)" and to one who uses centimetre as the unit it will be 1 cm = 84,(XX) cm.

Thus R J . = . n^P d istance ground distance

Converting Scales1. Find the R.F. when the scale is 2 inches to

the mile.2" = 1 mile2" = 63,360" (1 mile = 63,360 inches)Now the R.F. is always expressed in terms of a

fraction in which the numerator is one.

SCALES 11We have 2" = 63,360"

1" = 63,360/2 = 31,680 or, die R.F. is 1/31,680 or 1 : 31,680.2. Find the R.F. when the scale is 1" to 3 miles. 1" = 3 milesor, 1" = 3 X 63,360" = 190,080"So, R.F. is 1 : 190,080.3. Find the R.F. when the scale is 1 cenUmetre

to 1 Kilometre.*1 cm = 1 kmor, 1 cm = 100,000 cmSo, R. F. is 1 : 100,000,

scale o f a map is 1 centimetre = 1 kilometre. Find the scale in inches to the mile.

1 ^ntimetne = 1 kilometre = 100,000 centimetres The R. F. is 1 : 100,000.So, 100,000 inches would be represented by

1 inch

63,360 inches (1 mile) 1100,000

63,360 = 0.63 inch. The scale is 0.63 inch to the mile or 1" = l 58

miles.

5. The R. F. of a map is 1/1,000,000. What is the scale in terms of miles to the inch?

1 unit on the map represents 1,000,000 of ground or. 1 inch 1,000,000 inches of ground or, 1 inch represents 1,000,000/63,360 = 15.78

e , . miles.Scale IS about 15.78 miles to the inch.

Design and Division of Scales(0 The scale should always be expressed on a

map in all the three ways mentioned, i.e., (a) there should be a linear scale, (b) the scale should be stated in figures e.g., 1" = 1 mile, and (c) the R. F. should also be mentioned. On a manuscript map which is to be printed on the same size the scale may be indicated as above but if the map is to be reduced or enlarged for printing, the scale may be convenienUy shown only in a graphic form.

0 0 The length of the scale should be between 4 to 6 inches and thus a round number should be

guessed which could be represented by a length between 4" to 6".

(Hi) It is convenient to make the scale represent distance which is a multiple of 10.

(iv) There are two designs of Scale division

(a) Fully divided : The scale is divided into small divisions throughout its length.

(b) Open divided: The scale is divided into large divisions called primaries and the First primary on the left is subdivided into smaller divisions called secondaries.This ty pe is more convenient for drawing.

Use of G raphic Scale

(a) To measure distances between two points on the map : To use the scale for measuring the distance between two points on the map, take a sheet of paper and mark off the two points of the map on the edge of the sheet {see Fig. 3). Now apply this piece of paper on the scale so that the mark A coincides with zero of the scale {see Fig. 4), and the other point is found to lie between 4 and 5 mile marks. Now shift the piece of paper to the left and bring the B point to the 4th division and it is found that the point coincides with the secondary division marked 3/4. This shows that the length between thetwo points is 4 + -2. = 4 3 ^liles

4 4{b) To measure out a certain length from the

scale : Suppose the distance required is 8 miles.

u o f a n d mark on it the 8th point of the primary and the 3/4 point of the secondary division. The distance between the two points will be S i miles.

Distances could also be measured with the help of dividers.

I. Constructing Plain Scalesshow* "

100, 000 inches are represented by 1 inch.63,360 inches (1 mile)

*10millimetres=l centimetre. i .For devils of .s o fm e a su .,m ,,sa ,.d c o i S ,'S A ^ ^ ^

100,000 63,360 = 0.634."

1000 metres = 1 kilometre.

12 ELEMENTS OF PRACTICAL GEOGRAPHY

Fig. 3

Furlongs0 4 0

Fig. 4

It is seen that 8 miles will be represented by 8 X 0.634 = 5.07 inches or approx. 5.1 inches. Now this will be suitable length for drawing.

Draw a line of 5.1 inches and divide it into 8 equal parts with the help of the following method:

The line A B is equal to 5.1 inches* and it is to be divided into 8 equal parts.

From A draw a line A C so that the angle CAB is about 20 or 25. Now divide the line A C into 8 equal parts with the help of a pair of dividers.** Mark these points as a, b, c, d, e, f, g, and h. Join h to B and through the other points with the help of set squares draw lines parallel to h B. These will divide A B into eight equal parts.

Each of these primary divisions will represent one mile. Divide the first primary into 8 parts and each division (secondary) will represent 1 furlong, i.e., 220 yards.

In case of dividing a primary into secondaries the divisions required are small and so the following method is preferable.

At each end of the first primary which is to be divided, erect two perpendiculars one above the line and the other below i t (Lines drawn at any other angle can also be used, but the alternate angles should be equal). Mark off along these perpendiculars eight equal distances and join the points of division thus formed as shown in figure 5. The original primary

In Fig. 5 and all other figures of the chapter the dimensions of the lines A B etc., correspond to the original drawings which in printing have been reduced on 3 :2 or other proportions.

**If the line AC is taken to be equal to 4" then eight divisions can be made on it easily with the help of a scale by marking points at intervals of 1.2 inch.

SCALES

is thus divided into secondaries each of which in mis case represents one furlong.

13

Fig. 5

inn ydjrim aries and100 yd secondanes when the R. F. is 1/70,000.

1 represents 70,000 inches = 70,000/36 yd

r e p r e ^ t " would

1" represents 70,000/36 yd

6 " represents 35,00036 3

= ll,6662.yd

for < * convenientfor My scale drawing. Take, therefore, a round

in inches will represent it. Here the student should

Clearly understand that the round number is taken only for the convenience of the division of the scale and this number can be 8,000 or 12,000 or any other round number, but the length in inches that will represent it should not be either very small or too large for the size of the paper on which the scale is to be drawn. Supposing we do not take any round number, let us see what happens then.

The relation is that a length of 6 inches will repr^ent 11,666 2/3 yds. So take a line of 6 inches and divide it into six equal parts and each division will represent 1944 yds., one foot and two inches.

Obviously if we draw this scale, it will be very inconvenient to measure distances from it. In order to remove this difficulty a round number is always taken. ^

So, 35,000/3 yds. are represented by 6 inches

10,000 >ds. ^ 3 x 1 0 , 0 0 0 ^35,000

= 180 35

Tw . o =5.143 inchest o w a line of 5.14 inches and divide it into ten

represent 1000 yds. Divide the first pnmaiy into 10 equal parts and each Mcondaiy division will represent 100 yds. See

yards 1000 0

bnmEE1000 3000 5000 Yards9000

3. The scale of a map is 6" to 1 mile, t o w aWhat is

6" = 1 mile, or, 6" = 63,360 inches 1" = 10,560 inches.

So,R F = _ 110,560

Again, 6" = 1 mile, or. 6" = 8 furlongsDraw a line of 6 inches and divide it into eight

equal parts and each part will represent one furlong.

Fig. 6

win show" 'O ^ iee l parts and eachW ill snow one chain. See Fig. 7.

4. The R. p. = L1000 0 0 0 a scale toshow miles .ouu,uuo

1" = 1,000,000"

nr r - l/XX)X)00 ^63360 ~ (approximately).

But this is an odd number and so we take a round number of 90 miles and find out the length in mches that would represent iL

X


E 3Z Z EFurlongs

7 s I D

Furlong I 0

10C h a in s

15.8 miles are represented by 1"

90 15.8X90

F

Fig. 7

Furlongs 6 7

_45Q. = 5 69 inches 79

Draw a line of 5.7 inches and divide it into nine equal parts and each will represent ten miles. Divide the first primary into ten equal parts and each secondary division will represent one mile. See Fig. 8.

Miles10 10 20 30 40 50 60 70 80

Miles

Fig. 8

5. The R. F. is 1/100,000, draw a scale to read kilometres.

or1 cm = 100,000 cm 1 cm = 1 kilometre.

Draw a line of 12 cm and divide it into 12 equal parts so that each division will represent 1 kilometre. Divide the first primary into ten equal parts and each secondary division will represent 100 metres. See Fig. 9.

Metres 1000 O I

Imniini b

Kilometres 10 II

Fig. 9

6. Construct a scale of a field showing 100 links equal parts and each will represent 100 links. Divideto 1 inch. What is the R. F. ? the first primary into ten equal parts and each will

Draw a line of 6" length and divide it into 6 represent 10 links. See Fig. 10.

Links100

1 = 100 links or 1" = 22 yds. or 1" = 22 X 3 X 12 = 792"

100 200 3 00 4 0 0Links500

Fig. 10

R. F. = 1 : 7927. An area of 8 square inches in drawing

represents an area o f 512 sq. yds. Draw a

\

SCALES

o S " a i? f R- F-8 sq. in. = 512 sq. yds.1 sq. in. = 64 sq. yes.

or linch=V M =8yds.

15

. - . R F . = - - = _ L _(8 x 3 x 1 2 ) 188

Draw a line of 6" length and divide it into six equal parts and each division will represent 8 yds. Divide the first primary into eight equal parts and each will represent one yard. See Fig. 11

Y A R D S8 16 24

n. Comparative Scales

(a) Different Units

scale ';J?h /' ' ' i ' * Comparative^ ^ scale

R- F. = 1/50,000, i.e., 1" = 50,000"

Or, 1 " = ^ ^ = 1388.88 >ds.

number, say, 8,000 yds., and find the length in mches that would represent it.

are represented by 1"

36x8j000 i a a

Fig. II

323 Z

Y A R D S

40

In the usual way, draw a line of 5.07 inches and ^ ^ e it into eight equal parts and each will representl .C ^ yds. Divide the first primary into ten parts and each secondary division will represent 100 yds.

For the metre scale also the R. F. is 1/50,000. or 1 cm = 50,000 cm

or 1 cm = 500 metres.If we take a length of 12 cm., it will reptesent

6.(X)0 metres and when divided into 12 parts each m Wdl represent 500 metres. Dtaw this just below

Ih "* l>e lakenthat the zero point of the yard scale should coincidewith the zero point of the metre scale. See Fig 12

Yard 1000 0

^ra_L_ 500 0 Metres

thousand

^ ----- 1 ^ -= 1 P = l ------C=:rr , ----- ------- -

Hundred Metres

2- The statement on a French map is that one cenum etre represents one kilom etre. Draw comparative st^le to show kilometres and miles,

ro r the kilometre scale := 1 km or R. F. = 1 . ioq.ooq.

Draw a line of 15 cm and the whole length will re p ^ e n t 15 km. Divide it into 15 paru ^ T eT will represent 1 km. Sub-divide the fust n r i i ^ into ten parts and each will represent 100 metreT^

Fig. 12

For the mile scale :R- F. = 1 : 100,000 or 1 " = 100,000 inches.

100,000 inches are represented by 1 inch.

or 63,360 inches (1 mile) >


Divide this into ten equal parts and each will represent 1 mile. Sub-divide the first primary into quarter miles. Draw the kilometre scale and the mile

scale one above the other so that the zero points coincide. See Fig. 13.

Metres1000 0 I 2 3 4 5 6

Kilometres 7 8 9 10 II 12 13 14

a s8 4 0

Furlongs8 9

Miles

Fig. 13

(b) Time Scales1. A boy scout is marching at the rate of 3

miles an hour. Draw a scale for a map whose R. F. is 1/126,720.

1" = 126,720" = 2 miles, or, 6" = 12 miles.The rate of march is 3 miles an hour, so 12

MinutesSO 4 0 20 0H r i H I .

miles will be covered in 4 hours.Draw a line of 6 inches and divide it into 4

equal parts and each will represent one hours march. Sub-divide the first primary into 6 equal parts and each secondary division will represent 10 minutes march. See Fig. 14.

1Hours

3

3 2 1Miles

3

Fig. 14

9Miles

2. A cavalry is marching at the rate of 9 miles per hour. Draw a scale for a map of 1" = 3 miles :

9 miles per hour, i.e.. 18 miles in two hours. 3 miles are represented by 1".18 18= 6 inches.Draw a line of 6 inches which will represent 2

hours or 120 minutes march covering 18 miles.

Divide the line into 6 equal covering 18 miles. Divide the line into 6 equal parts and each division will represent 20 minutes or 3 mile march. Sub-divide the first primary on the left into 12 parts and each secondary division will represent 100 seconds and 2 furlongs. See Fig. 15.

Seconds 1200 61 20 40 60 80

Minutes100

P |H F24 18 12 6 0

Furlongs5 ,

Maas'

Fig. 15

(c) Pace ScalesDuring a rapid reconnaissance, it may not be

possible to use chain and tape due to shortage of time, and then distances can be measured with the help o f paces. The length of a pace of the person employed should be known and then the distance between any two points can be measured by paces. The standa^ military pace is of 30".

1. If the length of a pace is 30", draw a scale to

show yards and paces for a R. F. o f 1/10,560.R. F. is 1/10,560.or, 1" = 10,560", i.e., 6" = 1 mile.

63360.-. A length of 6" will represent

= 2,112 paces,

or, 2,112 paces will be represented by 1760 yds.

Z \

1,800 paces will be represented by

1300=1400 y d

Now 1760 yds. are represented by 6".

.1,500

SCALES 17

1,760X 1500.= 5.1 inches

Draw a line of 5.1 inches and the length will represent 1500 yards or 1800 paces. Divide it into ten equal parts and each division will represent 150 yds. and 180 paces. Further sub-divide the first primary into 10 equal parts and each will represent 15 yd. and 18 paces. See Fig. 16.

Yords Yards150 0 50 3 0 0 4 5 0 6 0 0 7 5 0 9 0 0 1050 1200 1350

180 O ISO 3 6 0 5 4 0 7 2 0 9 0 0 1080 1260 1440 1620S^eps Steps

Fig. 16

2. Draw a scale o f paces and metres when the R. F. is 1/15,000. Take 1 pace equal to 75 cm.

1 cm = 15,000 cm or =200 paces.

So a length o f 1 cm represents 150 metres and 200 paces.

So a length of 10 cm will represent 1500 metres and 2000 paces.

Draw a line of 10 cm, and divide it into 10 equal parts and each division will represent 150 metres and 200 paces. See Fig. 17.

'50 0 150 30Q 450 600 750 900 1050 1200 1350

EH200 0 200 400 600PACES 800 1000 1200 1400 1600 1800

PACES

Fig. 17

3. Draw comparative scales showing paces, yards and metres whens the R. F. is 1/7,200. Take 30 inches equal to one pace in case of the yard scale and 75 cm, equal to one pace in case of the metre scale :

(0 For Yard ScaleR. F. is 1 : 7,200

o f,l" = 7 3 (X )" = 2 M = 200w ls.36

Again 1" represents 7,200" or30

= 240 paces.

A length of 5" will represent 1,000 yds and 1,200 paces.

(,0) For Metre ScaleR. F. is 1 : 7,200or 1 cm = 7,200 cm = 96 paces.

So, 1 cm represents 72 metres and

= 96 paces12.5 cm = 900 metres and 96 x 12.5 =

_ . 1,200 paces.First draw a line of 5" and divide it into 10

equal parts and each division will represent 100 yds and 120 paces. Below this scale draw the metre scale i.e., draw a line of 12.5 cm, divide it into 10 equal p ^ and each division will represent 90 metres and 120 paces. See Fig. 18.

A .

lUrani ef Biiflaisii ......

18ELEMENTS OF PRACTICAL GEOGRAPHY

Metres 90

Y ords ' 0 0 1 ^ 2 0 0 300 ^qq sqq sq q 90O YardsI 1 I 1 F = 1 ------ i = ,

Paces 120CHH 360 ^ 80 600 720 640 960 1080 Paces

90 180 270 360 450 540 630 720 610 Metres

Fig. 18

(d) Revolution ScalesIf the country is suitable, distances can be

measured rapidly with the help of a bicycle. A piece o f tape is tied round the frontw heel and its circumference is found by trial of one complete revolution along the ground. The circumference can also be found from the formulae 2 nr where n = 22/7 and r = radius o f the wheel. The distance to be measured may now be covered by riding on the bicycle and the number of revolutions noted and the length can be ascertained by multiplying the number of revolutions with the circumference of the wheel.

1. A certain distance is covered by 1,220 revolutions of a bicycle wheel. Draw a comparative scale showing revolutions and yards for a sketch on a scale of 2" to 1 mile. The circumference of the wheel was 90".

1,220 revolutions will cover a distance of 1,220 X 2.5 = 3,050 yd. ( V 90" = 2.5 yd.)

For the convenience of scale drawing we take1.200 revolutions and it will represent a distance of1.200 X 2.5 = 3,000 yrd.

Now on the sketch 1,760 yrd are represented by

3,000 yrd will be represented by x

3,000 = 4.2 inches.So, a length of 4.2 inches will represent 3,000

yd and 1,200 revolutibns. Draw a line of this length; divide it into ten equ^l parts and each division will represent 300 yd and 120 revolutions. See Fig. 19.

yards3 0 0__ 0

h n - i120 0

Revolutions

12 15

Hundred Yards

21 24 27

120 2 40 3 6 0 ABO 6 00 720

Fig. 19

8 4 0 960 1000 Revolutions

III. Special TypesIf the contours on a map are drawn at an interval

of 100 feet, then the Vertical Interval (V.I.) is said to be 100 feet. The horizontal distance between two successive contours is the Horizontal Equivalent (H.E.), and, obviously, its length varies with the degree of slope. The steeper the slope, the smaller the Horizontal Equivalent.

A scale can be prepared to show the relation of the length of the Horizontal Equivalent to the degree of slope for a given Vertical Interval, so that if the Horizontal Equivalent is measured between two successive contours, the degree of slope can be read off directly from the scale.

From Fig. 20 it is seen that when the slope is 1 and the V.I. is one foot, the H.E. is 57.3 feet or say 20 yd.

This relation can be expressed in terms o f a formula for finding the length of H.E. for small angles.

H. E. = 2 0 x ^ ^ when D = degree of slope.

Now supposing the Vertical Interval (V.I.) is 100 feet, the length of the H. E. can be calculated for different degrees of slopes.

H. E. = 20x1001

20x1002

20x1003

20x100

= 2,000 yd for 1 of slope

= 1,000 yd for 2 of slope

= 666 yd for 3 o f slope

= 500 yd for 4 of slope

and so on.

X

SCALES 19

5 7 5

Fig. 20

If we are to prepare a scale of slopes for a map whose R. F. is 1/63,360 and the V. I. is 100 feet we first calculate the length of the H. E. as shown above and then draw a straight line and mark on it distances equal to 2,000 yd, 1,000 yd, if distances equal to2,000 yd, 1,000 yd, etc., in proportion to the R. P. of the map. In this case, when the R. F. is 1/63,360 the length in inches representing 2,000 yd can be found as follows :

R. F. is 1/63,360 i.e., 1" = 63,360" = 1,760 yd. or, 1,760 yd are represented by 1".

2,000 yd are represented by x 2,0001,760= 1.13 inches.

The length representing 2 will be of 1.13 inches and for 3 it will be^ of 1.13 inches and so on.

To construct the scale, draw a straight line and mark off successively the lengths representing the different degrees of slope. It should be borne in mind that the scale is for a particular Vertical Interval and for a given R. F. See Fig. 21.

V.I. = I00

Fig. 21

The same scale can be shown in a differentway.

Draw a line A B = 1.13 inches representing the horizontal distance between adjacent contours for a slope of 1. Now at A and B erect two perpendiculars A C and B D of equal length. Join C D and A D. To get the horizontal distance between adjacent contours for a slope of 2 \ bisect B D at E and from E draw a line E O parallel to A B. The line E O will represent the horizontal length for 2 slope. Similarly,

the lengths for other degrees of slopes can be obtained by proportionately dividing the line B D and drawing parallels from it. See Fig. 22. For instance, the mark for 3 on B D will have a length equal to | B D measured from D towards B; for 4 it will be j B D and so on.

V I . = JOQFig. 22

(a) Square Root ScalesSometimes in geographical maps for showing

the distribution of certain quantitative elements the use is made of circular graphs (also known as pie graph). Here the area o f the circle is made proportional to the quantities represented. The area of a circle being nr and the value of being constant, it is obvious that the radius will be proportional to the square root of the quantity.

Supposmg we are to prepare circular graphs showmg the acreage of cultivated land in different States of India, we shaU first have to find the square roots of the different acreages and draw circles proportionately, i.e., (take the radius for the Sq. root of 25,(XX),(XX) equal to one inch and the others are drawn proportionately). For the sake of convenience, a square root scale can be prepared so that the radius

\


of any can be measured on the scale and acreage represented by the circle determined.

Supposing the acreage in the different States varies from five million to fifty million. Now a scale can be drawn showing the square roots of 5 million, 10 million, 15 million and so on upto 50 million.

To proceed for actual drawing we find that the square root o f 25,000,000 is 5,000. Now we take one inch radius for representing the square root of

25,000,000 and calculate the length of the radius for others as follows :

The square root of 25,000,000 that is 5,000 represented by I".

The 5,000,000 that is 2235 inch

is represented by x 2,235 = 0.41 inch.5,000

Similarly, the square roots and the representing distances can be calculated (See Table 1).

T a ble 1

Figure Square root Representing distance, inch

10,000,00015.000.00020.000.00030.000.00035.000.00040.000.00045.000.00050.000.000

3,162'3,8734,4725,4775,9166,3256,7087,071

0.630.770.881.101.201.261.341.41

Draw a straight line and mark off these lengths as shown in Fig. 23.

5 10 20 30 40 50 Million rr M II Acres

Fig. 23

(b) Cube Root ScalesSometimes in statistical maps instead of circles,

spheres are drawn to represent different quantities. The volume of the spheres is proportional to the quantities represented by each sphere. Since the volume of a sphere is 4/3 kF or the cube roots of the quantities will be proportionate to the radii of the spheres.

Suppose we are to represent with spheres on a map of Uttar Pradesh the cities with population of one lakH or over. Here the radii of the spheres will be proportional to cube roots of the population figures.

We find that the population of the cities varies from one lakh to 5 lakhs. We suppose to represent

the cube root of 5 lakhs, i.e., 19.A by a radius of one inch. Now we take up cities with populations of less than 5 lakhs and calculate the cube roots for each and find out what would be the length of the radius for such and such cube roo t figure, remembering that 79.4 is represented by 1" (See Table 2).

TaBL 2

Number Cube roots Radius, inch

5 lakhs 4 3 2 1

79.4 73.7 66.958.5 46.4

1.000.920.840.730.58

A cube root scale can easily be prepared to show the variation on the length of the radius, and the population of any city can be determined directly by measuring its radius on the scale.

SCALES 21

To prepare the scale, draw a line of one inch length to represent the cube root of 5 lakhs, i.e., of79.4 and then mark off distances on it proportional to the cube roots of one lakh, two lakhs, three lakhs and four lakhs. These will be represented by 0.57,0.73, 0.84, and 0.92 inches respectively See Fig. 24. ^

2 3 4 5n I I I I

Lakhs Persons

Fig. 24

{c) Scales o f VerticalsAerial photographs are sometimes used for the

map to get a detailed information about the natural and cultural features of an area. The most common types are the vertical photos where the camera points vertically downwards and the details of the area appear in plan as in the case of map.

The scale of the photograph depends on the focal length of the lens and on the altitude from which the photograph was taken.

Referring to Fig. 25, find that the length A B,

PHOTO p i A

(Lens) 0 -

U. |UJ

i.e., half the photo represents C D on ground.

Si3

\ UJ,\

\

\ ::i \=i \i 1 |N

\I

GROUND_______C

Fig. 25

(d) Perspective ScaleA Perspective scale is used in landscape

drawingsblock diagrams, field-sketches, etc., (vide Chapter IV). A perspective scale decreases from the foreground to a vanishing point on the horizon (Vide Fig. 27) in which the lines A B, C D and E F are indicating the same elevation on the ground though they are decreasing in length.

So, the scale is AB CD

AB - BL - Focal length CD CL Altitude

. Focal length of lensAltitude (in the same unit)

Exam ple: Focal length of the lens of the camera is 8 inches and altitude 10,000 feet.

The sca le=-(10,000x12)" 1,20,000

- i.e., 4 2 inches to 8 miles.15,000

To prepare the scale draw a line of 4.2 inches; divide it into eight equal parts and each division will represent one furlong. See Fig. 26.

FURLONGS 7 8

f - H I

Fig. 26

rv. Diagonal ScalesA diagonal scale can be conveniently used for

dividing a short line into equal parts.Supposing the line A B which is equal to one

inch, is to be divided into ten equal parts. Draw two perpendiculars C A and D B of any convenient length andvmark ten small equal divisions on both C A and D B. Now, join the corresponding point of C A and D B by parallel lines. Join C to B by means of a diagonal line. If we drop perpendiculars on A B from the points of intersection of the diagonal with the paralled lines, the line A B will be divided into ten equal parts. The first small step from B to C on the right side of the diagonal C B is equal to 1/10"

2 2elem ents o f pra c tica l geography

HORIZON VANISHING POINT

50 0 4 0 0 300 200 '// 1 0 0 /

A

3/10

1/10

Fig. 28

Again draw a line A B equal to one inch and as in the previous case erect a rectangle C A D B and divide the sides C A and D B into equal parts by parallel lines. Now divide the bottom line A B and the top line C D into ten equal parts so that each division equals 1/10. Mark these divisions from the right to the left successively as 0, 1, 2, 3 and so on. Join the O point of the bottom line with the 1 point of the top, the 1/10 of the bottom with the 2 of the top and so on. The portion a at the bottom is equal to the portion jc y at the top and they are 1/10 in

length. Consider the line b x. The first step on the right o[ b X toward x y is equal to 1/10 inch = 0.01 inch and the second step equals 0.02 inch, the third0.03 inch and finally the line x y equals a b = O.l inch.

So with this arrangement, measurements upto 1/100 of an inch can be taken. See Fig. 29.

C D

Fig. 27

and the second step is equal to 2/10" and the third 3/10" and so on and ultimately the line C D is reached which is equal to A B. See Fig. 28.

1. Draw a diagonal scale of inches and measure a length of 2.67 inches.

Draw a line A B equal to 4" in length and divide it into 4 equal parts. Drop two perpendiculars C A and D B, and join C D. Now divide the sides C A and D B into ten equal parts and join the successive points with parallel lines. The original line A B was divided into four equal parts. Consider the portion on the extreme left and divide the top and bottom lines of this portion into ten equal parts. Now join successively the O of the bottom line 1 of the top, the 1 of the bottom with the 2 of the top and so on. The scale is complete and, to measure a length of 2.67 inches, place one leg of the divider at x and the other at y and the length x y is equal to 2 67 inches. See Fig. 30.

M etra .1 0 8 6 4 2 O 1

C 8 6 4 2 O

Fig. 30

X

SCALES 23

Now = xy = x p + p q + q y

^ . ^ . 2-=0.6".0.07".2" = 2.67.2. The R. F. o f a plan is 1/50. Draw a diagonal

scale to read metres and centimetres. R. F. = 1/5Q or 1 cm represents 50 cm.

or, a length of 2 cm will represent 1 metre.Draw a lien of 8 cm and it will represent 4

metres. Divide the line into four equal parts each division representing one metre. Subdivide the division on the extreme left to read up to 1/100 of a metre.

The length OP = 1 metre and 4 decimetres and 5 centimetres = 1.45 metres. See Fig. 31.

M etre

8 6 4 2

M etres

= J b

Fig. 31

3. The R. F. o f a plan is 1/50. Draw a diagonal scale to read yards, feet and inches.

R. F. = 1/50 or 1" represents 50".i.e., 1" = 50/36 = 1.4 yd (approx.).So, 1.4 yd are represented by 1".

8 yd " - ^ x 8 = 5.71".1.4

Draw a line o f 5.7 inches and divide it into 8 equal parts when each division will represent one yard. Erect a rectangle C A B D as shown in Fig. 32* and divide C A and D B into 12 equal parts. Now join the successive points by parallel lines. Consider the extreme division on the le f t This is equal to one yard or three feet. Divide the top and bottom lines o f the division into three parts, i.e., into three one-foot lengths and Join the zero of the bottom with one of the top and one o f the bottom with 2 o f the top and the 2 of the bottom with 3 of the top.

Feet2 I 0

C 32 I 0

Yards 6 7

t

' 1

3

Fig. 32

The line E F measures 2 yd 1 foot and 7 inches. EF = E K + KL + LF

= l y d + X y d + 2 y d 3 36

= 1 foot + 7 inches + 2 yds. = 2 yd 1 foot and 7 inches.

V. Vernier ScalesThe vernier is a device which enables a fraction

o f a division to be esUmated with accuracy. The Vernier Scale consists o f one small moving scale, the graduated edge o f which slides along the graduated edge of a larger scale, the primary scale. In Fig. 33, P is the Primary Scale and V the Vernier Scale. The method of construction of a Vernier will be clear from the following examples :

Fig. 33

(0 Construct a Vernier with a least count of1"

100 Draw a line O P and divide it into inches and

tenths as shown in Fig. 33. Draw a Vernier V V' on O P of length equal to 9 small divisions of O P. Now divide this length into 10 equal parts. Thus a smaU division of the Vemier scale is 1/100" shorter than a small division on a primary scale. In position(a) shown in Fig. 33 the zero of the Vemier scale coincides with the zero of the primary scale, and in

*In Fig. 32 F is at the right end of the anow whose left end is marked E

24e l e m e n t s o f p r a c t ic a l GEOGRAraY

this position the first division on the Vernier legs behind l/IO" of the first division on the primary scale. The second division legs 2.20" behind the second division on the primary scale. The third division on the Vernier scale lags 3/10" behind the third division of the primary scale, and so on; and the 10th division on the Vernier scale coincides with the 9th division of the primary scale. To read a length of say 3.86 inches slide the Vernier so that the zero of the Vernier coincides with the 3.8 mark of the primary scale. Now shift the Vernier just a litUe to the right so that sixth division on the Vernier comcides with primary scale graduation. The length indicated between the zero o f the primary scale and

the zero of the Vernier Scale equals to 3.86".(I'O Construct a Vernier with a least count of

one minute.In this case, the primary scale is divided into

degrees and half degrees. Construct a Vernier of the length equal to 29 small divisions of the primary scale and divide it into 30 equal parts. Thus the Vernier will read up to l/30th of half degree, i.e., one minute. In Fig. 34 the zero of the Vernier is placed a litUe to the right o f 23, and this little distance is equal to 25' because 25th mark on the Vernier coincides with a mark on the primary scale. Thus The reading is 23 + 25 = 23 25'. See Fig 34.

30 25 20

38

xe:36

J T I I I I I.28 26 22

Fig. 3420

VI. Enlargement or Reduction of Scales

This means the changing of the scale of a map or a portion of it. The enlargement is chiefly done(1) to get a base map on which details may be added ater by survey, and (2) to get more space for

labelling further information.Reduction might become necessary, say, to

combine four large scale maps into one.

(a) Square MethodThe method of enlargement or reduction is to

work by squares. The map to be enlarged or reduced IS divided into any suitable net work of squares. Then on a sheet o f paper squares are drawn representing the squares to be reproduced on the new scale p roportionate ly larger or sm aller. Enlargement or reduction is usually done by squares because certain maps are already divided into squares and the time of divide the map into squares and the time to divide the map into squares is saved. Otherwise any other convenient figure, e.g., a triangle can also be used.

After the original map has been divided up into squares and squares have been drawn on a fresh sheet o f paper proportionately larger or smaller

details are carefully transferred square by square. First the prominent marks like rivers, roads, railways, etc., are lightly sketched in and then other details are interpolated later.

So, calculation is only necessary to find out the size of the squares required on the new scale to represent the squares on the original, and size can be found out from the proportion :

N ew .scalp. _ ^O ld scale

E xam ple :

1. It is required to enlarge a 1 inch to one mile map into a 2 inch to 1 mile map. The original map is covered with one inch squares. It is obvious that the size of the squares for the enlarged drawing will be 2 inch squares.

2. To enlarge a map with a R. F. of 1/63 360 to one of 1/15,840.

1N ew scale _ 15.840 i

1----------- ----------- X 63,360 =4.O ld scale __ 1 15 ,84063360

Draw on the original map squares of 1/4 inch sides and the size of the enlarged squares will be 1 inch.

SCALES 25

3. To reduce a map with a R. F. o f 1/40,000,000 to one of 1/80,000,000.

1N ew scale _ 80,000,000 _ 40,000,000 _ \O ld scale _ 1 80,000,000 ~ 2 '

40,000,000Draw on the original map squares of 1 inch

sides and the size o f the reduced squares will be -j inch. See Fig. 35.

Fig. 35

(b) Similar Triangle MethodThis method is used for reducing or enlarging a

narrow area, such as a road, railway, river, canal which would otherwise be very difficult. Suppose in Fig. 36 the river between A and B is to be reduced on the scale of 8 : 3.

Join A and B by a straight line. Select a jx)int P at a convenient distance from A B; the further away is the point P, the more accurate will the proportions be obtained. Divide A P into 8 equal parts and from the third division from P draw C D parallel to A B. Join the bends and other specific points on the river to P; these points will be automatically fixed in the required proportion along C D; and other details can be drawn by observation. In the case of enlargement follow the method as shown along E P in the figure.

Fig. 36

(c) Instrumental MethodsThe instrumental methods of the reduction and

enlargement of maps involve the use of proportional compasses, pantograph, eidograph. Camera Lucida, P hotosta

Documents

elements of practical geography