5 Geographical data

Geographical data is, loosely speaking, data that relates to geographical co-ordinates and so can be plotted on a map. The wide range of online mapping tools now available means that it is possible to create a wide range of map-based representations from appropriate data sets very easily indeed. In this section, we will look at how to get data on to a map and then explore three different ways of visualising data on a map: proportional symbol maps, the rather exotic-sounding choropleth maps, and heat maps. We’ll also look at how the transformation of a map projection itself can be used to represent data in the form of a special sort of map known as a cartogram.

But first some orientation.