Cartography

Types of maps, their uses and symbols

What is a map?

• A 2-dimensional representation of a 3-dimensional object

• A generalized representation of the world

• No map is ever completely accurate or complete

General maps• Show a variety of base information• E.g. coastlines, settlements, rivers, landforms• Showing the base data is the chief function of

the map

Thematic maps

• Show a particular theme

• Other irrelevant information is filtered out

• Settlements, landforms, coastlines etc may also be show as points of reference

Thematic maps – choropleth maps

• Use colour to show differences in values between various areas

• Advantage: easy to read

• Disadvantage: can be too generalized

Thematic maps – proportional symbol maps

• Symbols are place on the map to indicate the location of specific data

• The size (proportion) of the symbols represents the quantity of the data

• Advantage: data is more location-specific

• Symbol sizes can be missleading

Using symbols that add meaning

Using 3D 0bjects

Proportional symbol map using pie charts

Thematic maps – isopleth maps

• Also known as contour maps

• Lines are used to connect data of the same value

• E.g elevation (height), temperature, pressure, humidity

Thematic maps – dot maps

• Dots are used to show the specific location of phenomena

• E.g settlements, shops, deaths, earthquakes

John Snow’s cholera map, 1854

Cartograms

• Thematic map• Area is substituted for

another value• Therefore shapes are

distorted• Not a true map since

scale is variable

Greenhouse gas emissions 2008

For more cartograms: http://www.worldmapper.org/index.html

Topographic maps

• Show a lot of detail• Show elevation (height)

above sea level• Useful for town and

country planners and hikers

Typical symbols on topographic maps

• Settlements• Communications• Natural features• Cultural features

All maps need:

• A scale• A compass, or at least an

arrow showing north. (not necessary on world maps)

• A key• Without these it is not a

map, it is instead a diagram or a figure

Scale

• Shows how large objects on the map are in the real world

• A map scale is therefore a ratio

Source: http://www.nrcan.gc.ca/earth-sciences/geography-boundary/mapping/topographic-mapping/10091

Scale

• Problem with small and large

• Small numerical scale e.g. 1:1000 = large scale map– Large scale maps show a smaller

area but greater detail

• Large numerical scale e.g. 1:500,000 = small scale map– Small scale maps show a larger

area but less detail

Ways of writing scale

1. As a ratio: for example 1/10,000 or 1:10,000– Advantage: easy to read– Disadvantage: becomes inaccurate when a map is copied

2. As a scale bar: for example – Advantage: easy to visualize– Remains accurate when map is copied– Disadvantage: some scale bars do not start at zero and

may be misinterpreted

The compass• Cardinal points: North

East South West

• N = 00

• E = 900

• S = 1800

• W = 2700

• Convention: north normally points straight up on a map (but not always)

True or magnetic north?

All maps use true northWhich corresponds to the Earth’s axis

Magnetic north True north

Review

• Using your course-book, find 2 examples each of the following:

1. A general map*2. A choropleth map*3. A proportional symbol map*4. A dot map*5. An isopleth map*

Then describe the main function of each map

*most of the maps in the course book are figures, since they do not have a compass, scale etc, but ignore this