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Maps

Chapter 2

Maps

⚫ Basic models and means of communication

used by geographers to depict the earth’s

surface.

⚫ Map – a representation, normally to scale and on a

flat medium, of a selection of material or abstract

features on, or in relation to, the surface of the

earth.

⚫ Map not drawn to scale?

Maps as the Tools of

Geography

• Maps are the primary tools of spatial analysis

• Cartography - The art, science and technology of

making maps

• All maps have some error (distortion) inherent

•3D space represented in 2D

The Geographic Grid

⚫ Set of imaginary lines that intersect at right angles to form a system of reference for locating points on the surface of the earth

⚫ Position on the Earth is determined by the grid system of latitude

and longitude and are measured in:

⚫ degrees, minutes and seconds -

⚫ 45° 27’ 15”

⚫ decimal degrees

⚫ 45.4542

⚫ Key reference points⚫ North and South Poles, (90° N & S)

⚫ Equator (0 °)

⚫ prime meridian (0°)

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The Geographic Grid

⚫ Latitude

⚫ Angular distance north or south of the equator

⚫ Measurements ranging from 0°(equator) to 90° (poles)

⚫ Lines (parallels) are parallel and run east-west

⚫ Distance between each degree ≈ 69 miles

⚫ Can be subdivided into minutes and seconds

The Geographic Grid

⚫ Prime meridian (0°)

⚫ Starting point for east-west

⚫ Passes through Greenwich, England

⚫ Longitude

⚫ Angular distance east or west of the

prime meridian

⚫ Measurements ranging from 0° (prime

meridian) to 180°

⚫ Lines (meridians) are farthest apart at

the equator and converge at the poles

The Geographic Grid

⚫ Time depends on longitude

⚫ Greenwich mean time (GMT)

⚫ Time at the prime meridian

⚫ International Date Line

⚫ Where each new day begins

⚫ Generally follows the 180th meridian

Map Projections

⚫ Earth can be represented with reasonable accuracy only on a globe

⚫ Globe properties⚫ All meridians are equal in length

⚫ All meridians converge at the poles

⚫ Lines of latitude are parallel to the equator and to each other

⚫ Parallels decrease in length as one nears the poles

⚫ Meridians and parallels intersect at right angles

⚫ The scale on the surface of the globe is the same everywhere in all directions

Map Projections

⚫ A map projection is the mathematical transformation of space from the surface of the earth to that of a flat plane.⚫ curved surface of the earth, on a flat medium

⚫ some distortion is inevitable

⚫ Distortion - least for small areas and greatest when a map attempts to show the entire surface of the Earth.

⚫ All flat maps distort some or all of the four main

properties of actual earth surface relationships:

⚫ Area

⚫ Shape

⚫ Distance

⚫ Direction

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Map Projections

⚫ Greenland vs. South America

⚫ Which one is bigger?

Map Projections

⚫ Equal-area (equivalent) projections

⚫ Areas are in correct proportion to earth reality

⚫ Shape is distorted

Map Projections

⚫ Conformal projections - Shape

⚫ Shapes of small areas are accurately portrayed

⚫ No projection can provide correct shapes for large areas

⚫ Area is distorted

Map Projections

⚫ Equidistant projections - Distance

⚫ Distances are true in all directions from one or two

central points

⚫ Distances between all other locations are incorrect

⚫ A map cannot be both equidistant and equal-area

⚫ Robinson projection

⚫ Compromise between equal-area and conformal

⚫ Fairly realistic view of the world

⚫ Distortion is greatest in less populated places

(N. Canada

Greenland

⚫ Russia)

⚫ US 3%

smaller

⚫ Canada

21% larger

Map Projections Scale

⚫ Ratio between the measurement of something

on a map and the corre-

sponding measurement

on the earth

⚫ Represented in three ways

⚫ Verbal

⚫ Graphic

⚫ Representative fraction

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Scale

⚫ Can range from very large to very small

⚫ Large-scale maps

⚫ A large scale map covers a small area and shows

great detail.

⚫ Ratio of map to ground distance is relatively large

⚫ RF is large, e.g. 1/10,000

⚫ Small-scale maps

⚫ A small scale map covers a large area and shows

only large or prominent features.

⚫ Ratio of map to ground distance is smaller

⚫ RF is small, e.g. 1/100,000,000.

Effects of Scale

⚫ Scale controls not only how features are shown, but what features are shown. ⚫ Scale also controls the level of detail and hence the purpose of

the map.

Types of Maps

Topographic Maps and Terrain

Representation

⚫ Topographic maps are general-purpose maps

⚫ Depict the shape and elevation of terrain

⚫ Natural and human features

⚫ USGS topographic map series

⚫ Depicting relief (variation in elevation)

⚫ Spot heights

⚫ Contour lines

⚫ All points along line are of equal elevation above a datum

plane, usually mean sea level

⚫ Contour interval is the vertical spacing between contour lines

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Thematic Maps and Data

Representation

⚫ Thematic Maps: a map that

shows a specific spatial

distribution or category of

data

⚫ Qualitative maps

⚫ Show the distribution of a

particular class of information

⚫ Locations of oil fields, national

parks or crop specialization

Thematic Maps and Data

Representation

⚫ Quantitative maps

⚫ Show the spatial characteristics of numerical data

Thematic Maps and Data

Representation

⚫ Point symbols

⚫ Dot maps

⚫ Each dot represents a

given quantity

⚫ Graduated symbol

maps

⚫ Size of symbol varies

according to quantities

represented

Thematic Maps and Data

Representation

⚫ Area cartograms ⚫ Areas of units are drawn proportional to the data they

represent

⚫ Left: Traditional view of the election

⚫ Right: Size proportional to population – instead of land area

States are sized

Relative to the

Number of residents.

Thematic Maps and Data

Representation

⚫ Line symbols

⚫ Various symbols represent features that have length

but insignificant width

⚫ Examples?

⚫ Isoline maps

⚫ Lines of constant value

⚫ Flow-line maps

⚫ Portray linear movement between places

Map Misuse

⚫ Message conveyed by a map reflects the intent and, perhaps, biases of its author

⚫ Techniques for making misleading maps⚫ Lack of a scale

⚫ Simple design that omits data or features

⚫ Colors with a strong psychological impact

⚫ Bold, oversized, and/or misleading symbols

⚫ Action symbols

⚫ Selective omission of data

⚫ Disinformation

⚫ Inappropriate projection

⚫ During Cold War – Russia admittedly falsified information on their public maps.

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Remote Sensing

⚫ Obtaining images of an area from a distance

⚫ Aerial photography⚫ Standard photographic film

⚫ Infrared film⚫ False-color images

⚫ Nonphotographic imagery⚫ Thermal scanners

⚫ Radar

⚫ Lidar (light detection and radar

⚫ Satellites⚫ Landsat satellites

Geographic Information

Systems (GIS)

⚫ Computer-based set of

procedures for gathering, storing,

manipulating, analyzing, and

displaying geographically

referenced data

⚫ Geographic database

⚫ Digital record of geographic

information

⚫ Maps, surveys, aerial photos, satellite

images, etc.

⚫ Purpose of study determines data

World Health Threats

⚫ Cholera

⚫ Dr. John Snow –

created first crude GIS

⚫ Overlaid map of cholera

victims over map of

water pumps and

streets.

Applications of GIS

⚫ Various fields for a variety of purposes, including:

⚫ Biologists and ecologists: studying environmental

problems

⚫ Epidemiologists: studying diffusion of diseases and

entomological risk factors

⚫ Political scientists: evaluating legislative districts

⚫ Sociologists: examining patterns of segregation

⚫ Private sector companies: site selection, analyzing

sales territories, calculating optimal driving routes

⚫ Government: transportation planning, analyzing

patterns of crime, responding to disasters

Virtual and Interactive Maps

⚫ Maps are widely available on the internet

⚫ Google Earth

⚫ Combines aerial photos, satellite images, and maps

with street, terrain, and other data

⚫ Mashups

⚫ Digital maps merged with data from other sources

⚫ Interactive mapping