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Creating a choropleth map

A commonly required task is to create a map where the areas or polygons on the map are shaded according to their attribute values. This type of shaded area map is called a choropleth or a thematic map. Attributes can be continuous or categorical. The shading technique and classification scheme employed must be carefully selected as they can both greatly influence the spatial patterns portrayed in the map.


Two relevant examples might be where a researcher wishes to map the states in the USA, firstly shaded according to which sub-region they are in, and secondly shaded according to their population density. The first would be an example of a choropleth map of categorical data, the second a choropleth map of continuous data.