A map makes it possible to overview a large geographical area. A thematic map is often limited to illustrating the spatial distribution of a single phenomenon such as temperature or population density.
Choroplethic maps are special thematic maps which have many similarities with digital images.
Chorological mapping methods are used today in digital image processing. A simple example of settlement mapping may illustrate this. Settlement density can be mapped chorologically by spreading a grid over a topographical map. The number of houses is counted in each square. The result of the count is a Chorological matrix consisting of numbers placed in a co-ordinate system.