PPT Slide
Choropleth Maps are also called “Shaded”. The Class of data is Area, Scale of Measurement is Numerical, and the Graphic Element is Shade.
Choice of categorization method and number of classes is critical. Use basic statistics, frequency curves, or histograms to determine which method best suits your purpose. There is no one right way but some methods are better than others!
Choropleth maps should only be made with Derived data. Different size areal units [states, counties, etc.) give a false impression. Derived data eliminates the problem of unequal areas.