Range Graded Proportional Circle Map

http://pubs.usgs.gov/fs/fs-004-03/
A range graded proportional circle map is a proportional circle map in which the data are divided into groups, using classification methods common to choropleth mapping. The cartographer chooses symbol sizes for the different classes so that the map reader can easily identify different circle sizes, and thus, categories of the data being examined. This type of circle map deals with more than one type of data. 
The range graded proportional circle map shown above features the river characteristics, according to the notes found in Lewis and Clark's journal(s). The areas of the circles are proportional to the river/channel width.