Baron P. C. Dupin

Geography (U.G), SEM- II, Paper – C4P : Thematic Map: Choropleth Map

(6 October 1784, Varzy,

Nièvre – 18 January

1873, Paris, France)

Baron P. C. Dupin

Definition: Thematic mapping is when a geographical pattern of spatial information on a particular subject or specific

data themes in a geographic region is displayed on a map. When expressed in a map, the map is called

thematic mapping. This form of map is closely related to geovisualization.

Characteristics: 1. Information on various geographical or socio-economic issues is first collected and then published on

such maps.

2. The temporal average change of any information of a region i.e. annual, monthly, seasonal i.e. - winter

or summer allowance can be published on thematic or thematic map.

3. This map is also called a special-purpose, single-topic, or statistical map.

4. This map focuses on the spatial variability of a specific distribution or theme (such as population

density, crop intensity, or average annual income), whereas a reference map focuses on the location

and names of features.

5. This map shows the spatial distribution of one or more specific data themes for selected geographic

areas.

Importance: 1. This form is used for map thematic research.

2. All natural, economic and population related information can be collected.

3. Since this map is statistically based, it is possible to present this figure scientifically.

4. In such a map it is possible to represent any subject by color, line, dot and circle.

5. It is possible to gain knowledge about natural, economic and social issues through reading such maps.

6. It is possible for ordinary people to understand that such map reading is very easy.


Example: - Choropleth map, Contour line Map, Isotherm Map, Isohyetal Map, Heat map, Dot

distribution map, Proportional symbol maps, Population Map, Animated time-series map

etc.

Purpose: -

i. Educational, ii. Research, iii. Developmental etc.

Principles of thematic mapping:

The principles or methods to be used in preparing this form of map are the main

ones –

1. Point: Points of different sizes to show the size of geographical statistics (such

as population, city, city, metropolis, etc.); Symbol; It is used.

2. Line: To show inequality in the flow of passengers, goods, vehicles, etc.

3. Diagram: Various signs or diagrams are used to show the amount of different

regions such as wetlands, deserts, forests, agricultural areas, etc.

Manufacturer:

The head office of National Atlas and Thematic Map Organization (NATMO) in

India is located at Sector-5, Salt Lake, Kolkata.



Choropleth maps are the primary popular tools of human geographers. According to

F. J. Monkhouse and H. R. Wilkinson, “If the isopleths is the chief tool to

climatologist, the Choropleth may be said to be the chief tool for human

geographers”.

Literally meaning: The word „Choropleth‟ consists of two Greek words such

as “choros” meaning “area / region / space” and “plethos” meaning “multitude /

crowd”, the full meaning of which is - “field or country insertion”

Definition: Such a map is a thematic mapping or technically quantitative regional map where

the intensity of an element (e.g. population, settlement, grain production, per-capital

income, road and river length, etc.) by graded shading or color system following the

boundaries of the respective administrative unit or the spatial or linear distribution

of density is measured in terms of per unit administrative field (ratio between

element and administrative field). This form is also called Quantitative Area Map

and Choropleth Heat Map as the number of elements per unit area is expressed in

numbers.


The Choropleth map was first created in 1826 by French

mathematician and engineer Baron Pierre Charles Dupin, to

illustrate the availability of basic education in France under the

name "cartes teintées" (colored map in French). But the term

“Choropleth map" was first introduced in 1938 by the

geographer John Kirtland Wright. This map is now relatively

easy to create using GIS, spreadsheets, or other software tools.

Principal: The basic principle of Choropleth map is that the intensity of color or shading is directly

proportional to the density of the elements. That is, if the color or shading is light or thin, the

average value of the material per square unit is less. Similarly more dense shadows indicate

higher density of the material.

These density maps, like the administrative units, show only the average distribution. Thus,

the grouping of several administrative units under an average value demonstrates the

distributional unity. Clearly, the wider the units in the administrative regions, the more agile

the generalizations presented in the form of maps. Again, the lower the administrative zones,

the more accurately it will be possible to accurately represent the regional distribution of

material, otherwise the nature of the distribution will become too generalized.

(1891–1969)

(1784 – 1873 )


Method: The construction of a Choropleth map is done in six steps. E.g. –

The first step is to draw a worksheet with six columns, serial number in column – 1, the

name of the unit in column – 2, the field in column – 3, the absolute value of each element in

column – 4, the density or intensity in column – 5, and finally the administrative in column –

6. Grade row of units.

Secondly, determine the density or intensity according to the objective. Density (ρ) is the

ratio of the area of an administrative area with the extreme value of a particular element in

the respective administrative area.

Densit (𝜌) = The ultimate value of a particular element in the respective administrative areaThe field of the said administrative area

Crop intensity, on the other hand, is the percentage of the ratio between total cultivable land

(GCA) and actual cultivable land (NCA). That is –

Crop intensity (𝜌) = Total cultivable land in the respective administrative area (GCA) Actual farmland of the said administrative area (NCA) × 100


In addition to maintaining the quality of the land, farmers in India and other major

agricultural countries of the world are now focusing more on seasonal and annual

cropping to maintain productivity in order to meet the widespread food demand. The

farmer cultivates the land more than once a year and once or twice a year according to the

productivity of his land. The Gross Cropped Area (GCA) is the geographical area that a

farmer has and the amount of land that the farmer grows in that geographical area is the

Net Cropped Area (NCA). The intensity of cropping is measured by the ratio of these two.

In this way we can measure the road density, drainage density etc. of a region and display

it as a map.

Thirdly, to determine the number of classes and class-differences according to the

objectives. The first step in determining the class-interval is to select the class number, which,

although there are multiple methods, H. A. Sturges' method of determining the class

number is the most acceptable. Which is –

Number of class (K) = 1+3.322.log N (Where, K = Number of Class, and log N = Logarithm of total number of observation/items.)

Class-interval is the ratio between the class number and the range of material distribution.

The distribution range is the difference between the maximum and minimum values of the

material. The formula for class interval (i) is -

Class intervel (i) ( = 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒 (𝐻)−𝑀𝑒𝑛𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒(𝐿)𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑙𝑎𝑠𝑠 (𝐾)

Fourthly, determine the class structure. Class formation is done in two ways, viz.

a. Exclusive method:


This is an uninterrupted actual class-spacing method. In this

method the actual class interval is determined from the

difference between the values of the lower class boundary and

the upper class boundary of each class. In this case, the value of

the upper class boundary of any previous class is equal to the

value of the lower class boundary of the next class, so the

distance between the two is always zero (0). Such as - 10-20,

20-30, 30-40, etc. It is important to note that in such a case, if

the value of an element is in the upper limit of a class, then in

the statistical division that element is included in the next class.

Classes Class

Interval Lower Upper

0 10 10

10 20 10

20 30 10

30 40 10

40 50 10

50 60 10

b. Inclusive method:


It is better to follow the exclusive method in case of this form map. Because in this

method the free edge class can be formed. Depending on the homogeneity and

inconsistency of the centralization of the distribution of the material, the class gap can

be equal and unequal respectively.

However, it should be noted here that if the density of elements in one or two areas of an

administrative area is much higher than that of other areas, then the density of elements

in the remaining areas can be divided into residual class-spacing. This method can be

used in the same way in the case of more dense material concentrations.

The method by which the class interval is determined from the

difference between the value of the lower class limit and the

upper class limit of each class. Such intervals are not used as

actual class intervals. In this case, just as the value of the upper

class limit of any previous class and the lower class limit of the

next class immediately after it differs, so the difference between

the two is always one (1), e.g. - 10-19, 20-29, 30-39, etc. This

type of class boundary is called stated class limit.

Classes Class

Interval Lower Upper

10 19 9

20 29 9

30 39 9

40 49 9

50 59 9

60 69 9

Fifthly, the step is to construct a Choropleth table where the class of density or

intensity class is shown in column – 1, the shading system (Grade) in column – 2,

the name or serial number of the administrative unit in column – 3, and the

comments/remarks in column – 4.

Sixthly, prepare Choropleth map by fine/meticulous drawing of shades (both

shading or color) following the administrative boundaries according to the

Choropleth table.


Characteristics: 1. Such a map shows the intensity or density of the physical and spatial distribution

of any material according to the administrative boundaries.

2. Periodic shades or colors are used to denote low to high density in such maps.

3. In such a map, the density of the shadow or color density is always maintained

with the density of the material. 4. Such a map represents the variability of the

desired measure across an area.

4. This maps can also be constructed to represent the deviation of the data from its

average.

5. These maps are drawn to represent certain changes also.

Merits or advantage: 1. This map shows the comparative distribution of specific elements in a particular administrative area.

2. This map is very effective in representing the population density, sex ratio, percentage of population

growth, urban or rural population ratio, percentage of total cultivated land, percentage of wheat under

total cultivated area, etc.

3. This map is very important in representing sudden variable factors such as population density, crop

intensity, etc.

Demerits or disadvantage or Limitation: 1. In the case of this form map, it is recommended not to have open class-edge in case of equal class-spaced

class. But unequal class-spaced classes may have open edges.

2. It is recommended to draw this form map by selecting periodic shades or colors.

3. This map is drawn following the administrative division and its boundaries but most of the geographical

elements change according to the natural division, in which case this map can create a situation of

misunderstanding.

4. This map is often not suitable for showing total values. Proportional symbol overlays (included on the

Choropleth map above) are one solution to this problem.

5. It can be difficult to distinguish between the shades used in this map.

6. In this map where we see a sudden change in the density or intensity of the material moving from one shade

to another where in nature, these changes are seen to occur gradually in sequence.

7. The extreme values within the class-interval are shown in this map by the same shade / color which is

misleading.

8. The differences between the units on the map are hidden and for this reason, smaller units are better than

larger ones.

9. This map gives a false impression of abrupt change at the boundaries of shaded units.



Gray scale progression

The leading common color used in the Choropleth map.

Single hue progression

Partial spectral progression

Bi-polar color progression

Qualitative color progression

Full-spectral color progression


Periodically selected shades used to draw of Choropleth maps

Den

sity

In

cise

For Class -3 For Class -4 For Class -5 For Class -6 For Class -7

Choropleth Map Q. Prepare a Choropleth map to show the ratio of total population and area of respective

CD blocks of the Jhargram Dist. (2011) according to the given data:


Sl.

No.

Name of C.D.

Blocks

Area

sq.km.

Total population

1 Jhargram 515.11 170097

2 Binpur-I 357.62 156153

3 Binpur-II 583.50 164522

4 Jamboni 318.83 113197

5 Nayagram 501.44 142199

6 Sankrail 276.80 115418

7 Gopiballavpur-I 275.83 108254

8 Gopiballavpur-II 192.17 104996

Jhargram

Jhargram

Binpur – I

Gopiballavpur - I

Gopiballavpur - II Sankrail

Nayagram

Binpur - II

Jamboni

0 20 10

Km.

20


Sl.

No.

Name of C.D.

Block

Area (Sq.

Km)

Total

population

Population

density per

Sq. Km.

Grade

1. Jhargram 515.11 170097 330.215 IV

2. Binpur I 357.62 156153 436.645 II

3. Binpur II 583.50 164522 281.957 IV

4. Jamboni 318.83 113197 355.039 III

5. Nayagram 501.44 142199 283.581 IV

6. Sankrail 276.80 115418 416.973 II

7. Gopiballavpur I 275.83 108254 392.466 III

8. Gopiballavpur II 192.17 104996 546.370 I

Step – 1: Calculation table for Choropleth map


Step – 2: Calculated the population density of respective CD block of Jhargram Dist.

Densit 𝜌 = The ultimate value of a particular element in the respective administrative area(𝑃𝑇)

The field of the said administrative area (𝐴)

For example of Jhargram CD Block

Population Density (𝜌) = 𝑃𝑇𝐴

Or, Population Density (𝜌) = 170097 persons 515.11 𝑠𝑞.𝑘𝑚. = 330.215 persons per sq.km.

Step – 3: Calculated the number of class according to H. A. Sturges formula

Number of class (K) = 1+3.322.log N (Where, K = Number of Class, and log N = Logarithm of total number of observation..) Or, Number of class (K) = 1+3.322.log 8

( Here N = 8 because number of CD block is 8) Or, Number of class (k) = 4.000064937

So, Number of class (k) is 4 (Round off)


Step – 4: Calculated the class intervel

Class intervell (i ) = 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒 𝐻 − 𝑀𝑒𝑛𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒(𝐿)𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑙𝑎𝑠𝑠 (𝐾)

Or, Class intervel (i ) = 546.370 − 281.9574

Or, Class interval (i) = 264.4134 = 66.10325 Persons

So, class interval is 66 persons (Round off)

Step – 5: Determine the class structure or formation in Choropleth table

Step – 6: Meticulous drawing of shades or colour

Population density (persons/sq.km.) class

Grade Serial Number of C.D. Blocks

Remarks

< 348 IV 1, 5, 3 Exclusive method is

applied to form

classes which have

two open ends.

348 – 414 III 4, 7

414 – 480 II 2, 6

> 480 I 8

KEY

Name of C.D. Block

1. Jhargram

2. Binpur I

3. Binpur II

4. Jamboni

5. Nayagram

6. Sankrail

7. Gopiballavpur I

8. Gopiballavpur II

Showing The Population Density Of Different C.D. Block Of Jhargram District (2011)

20 10

Km.

20 0


LEGEND

> 480

348 – 414

< 348

414 – 480

Population density per sq.km. 1

2 3

4

5

6 7

8

(Gray scale progression)


KEY

Name of C.D. Block

1. Jhargram

2. Binpur I

3. Binpur II

4. Jamboni

5. Nayagram

6. Sankrail

7. Gopiballavpur I

8. Gopiballavpur II


10

Km.

20


20 0

LEGEND

> 480

348 – 414

< 348

414 – 480


2

3

4

5

6

7

8

(Single hue progression)


Procedure of Choropleth map Drawing

Step – 1 Step – 2


In my personal opinion, the single shade or color progression method of determining the

Choropleth map is the most acceptable. This is because the reader of such a map can easily

identify the areas with the lowest density from the highest density regions without looking at

the map indicator (Legend or Index or key).

The method of drawing Choropleth map in Single shade progression method is as follows -

First of all the number of lines of shading should be multiplied in geometrical proration

method in the respective administrative areas of low density to high density according to the

grade, viz. , 1,2,4,8,16,32,64 etc.. Then, if we think that the spacing between the lines is 0.1

inch, then if a line is drawn at a distance of 0.1 inch in the low density shading area, then in

the next high density region, two of those equivalents, 4 for the next grade, and 8 for the next

grade. At the same time, the number of lines and the density also increases. However, the

difference between the two lines in the area where the lowest grade is present depends on the

cartographer. This gap is arbitrary (but it is important to keep in mind that the map is visually

appealing), but the shading process is done by drawing lines according to the same angular

meaning and in parallel with the grade of all the respective administrative areas. Which is

shown in the previous slide.

Procedure of Choropleth Map Drawing by Single Shade Progression Method

KEY

Name of C.D. Block

1. Jhargram

2. Binpur I

3. Binpur II

4. Jamboni

5. Nayagram

6. Sankrail

7. Gopiballavpur I

8. Gopiballavpur II


10

Km.

20


20 0

LEGEND

> 480

348 – 414

< 348

414 – 480


2

3

4

5

6

7

8

(Qualitative shade progression)

KEY

Name of C.D. Block

1. Jhargram

2. Binpur I

3. Binpur II

4. Jamboni

5. Nayagram

6. Sankrail

7. Gopiballavpur I

8. Gopiballavpur II


10

Km.

20


LEGEND

> 480

348 – 414

< 348

20 0

414 – 480


2

3

4

5

6

7

8

(Single shade progression)


Choropleth in the map of the Jhargram district depicts the population density of different

CD blocks. From the map, it can be interpreted that the distribution of population

density in each CD block of Jhargram District is quite uneven. Gopobolovpur-II CD

block has maximum population density - about 546 people per sq.km. And the lowest

population density is seen in Binpur - II CD block - 282 people per sq.km. Although

Binpur-I, Sankrail, Gopiballavpur-I, and Jhargram CD blocks have not to highest

population density, the population density in this part is quite high - 348-480 people per

sq.km. Also, the population density of the remnant of Jhargram block is a slight decrease

of 348persons per sq.km., which indicates that uneven distribution of natural resources,

discriminatory topographical terrain, poor livelihoods, inadequate communication

systems, as well as economic development are not very high level in the district.

Interpretation

Sl No. Tehsil (CD Block) Area (km²) Population (2011)

3 Chandrakona I 196 1,72,001

4 Chandrakona II 171 1,46,898

5 Dantan I 257 1,72,107

6 Dantan II 187 1,55,017

7 Daspur I 171 2,03,987

8 Daspur II 162 2,38,529

9 Debra 368 2,88,619

10 Garbeta I 421 2,28,513

11 Garbeta II 353 1,48,410

12 Garbeta III 304 1,69,528

13 Ghatal 216 2,86,264

18 Keshiary 293 1,49,260

19 Keshpur 499 3,39,248

20 Kharagpur I 229 4,65,644

21 Kharagpur II 256 1,83,440

22 Midnapore 327 3,60,969

23 Mohanpur 133 1,11,901

24 Narayangarh 510 3,02,620

26 Pingla 244 1,94,809

27 Sabang 296 2,70,492

28 Salbani 554 1,88,653

Data Source link: https://censusindia.gov.in/2011census/dchb/DCHB_A/19/1918_PART_A_DCHB_PASCHIM%20MEDINIPUR.pdf


1 .Chandrakona I

2. Chandrakona II

3. Dantan I

4. Dantan II

5. Daspur I

6. Daspur II

7. Debra

8. Garbeta I

9. Garbeta II

10. Garbeta III

11. Ghatal

12. Keshiary

13. Keshpur

14. Kharagpur I

15. Kharagpur II

16. Midnapore

17. Mohanpur

18. Narayangarh

19. Pingla

20. Sabang

21. Salbani

1 2

3 4

5 6

7

8

9

10

11

12

13

14 15

16

17

18

19

20

21

Paschim Medinipur

Km.

Q. Prepare a Choropleth map to show the total population respect of area of different CD blocks of the

Paschim Medinipur Dist. (2011) according to the given data:

Key

https://censusindia.gov.in/2011census/dchb/DCHB_A/19/1918_PART_A_DCHB_PASCHIM MEDINIPUR.pdf











Reference:

1. Misra, R.P., Ramesh,A., 2002, Fundamentals of Cartography, Revised and Enlarged, pp. 473-475

2. Monkhouse, F.J., Wilkinson, H.R.,1976, Maps and Diagrams, Methuen & Co LTD, London, pp. 332-352

3. Sarkar, A., 2009, Practical Geography, revised edition, orient black swan, Kolkata, p.180.

4. Sing, R.L., Sing, R.P.B., 2014, Elements of Practical Geography, Kalyani Publishers, New Delhi, pp. 180-181.

5. https://en.wikipedia.org/wiki/Choropleth_map

https://en.wikipedia.org/wiki/Choropleth_map

https://en.wikipedia.org/wiki/Choropleth_map

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Baron P. C. Dupin