Range Graded Proportional Circle Map

Range graded proportional circle map, not to be confused with the below continuously variable proportional circle map although they are quite similar.  In range graded proportional circle maps the data is divided into groups.  Then, the mapmaker, or cartographer, chooses circle sizes for adjacent class so that the reader of the map can easily see the difference in circle sizes.  The map seen above is a range graded proportional circle map of the population of Chicago with German ancestry in 1990.

The map URL is: http://www.neiu.edu/~nerobert/391/cartographic.htm