Proportional circle map

http://personal.frostburg.edu/sbriggs0/maps.htm
Proportional circle maps are similar to dot density maps.  The main distinguishing feature of a proportional circle map is the variability in the size of each circle.  Depending on the key provided for a given map, each circle size depicts a value.  This proportional circle map depicts the number of walmarts in a state, the largest circles represent 100 walmarts!