GIS Files 4: Putting it all in a system

4.2: GIS reveals all (1)

The thematic map

By bringing together data from a wide range of different sources, you can visualise trends in the data by creating thematic maps. How does this work?

We discussed in previous chapters how a GIS display of map information is very flexible. Unlike a paper map it does not require every piece of information to be visible at the same time. It can also change the depiction of a particular object depending on the value of one of its attributes. This function is known as thematic mapping. You will already be familiar with thematic maps from atlases and geography textbooks. For example, a map of parliamentary constituencies shaded in different colours can show the number of seats held by different political parties. GIS can build this kind of map automatically from the data values (number of seats), and in many different ways.

Thematic maps come in all shapes and sizes, for example:

• a map of farmer's fields showing a different colour for each type of crop grown;

• different sized point symbols to show the relative population of towns;

• a display of a road network with different colours to show average traffic speeds; and

• a density map to show average numbers of badgers across different counties.

These examples are typical of the types of thematic mapping for which GIS is used. The really dynamic thing about these maps is that they can automatically change their appearance as the values in the data tables change with time. Hence, you can use this kind of mapping to constantly monitor traffic flow.

Illustration of changing traffic congestion

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