Proportional Circle Map - Walmart 2007

http://personal.frostburg.edu/sbriggs0/maps.htm

Proportional circle maps use the relative size of circles to represent different variables.  For example, smaller circle sizes can represent a small magnitude of the variable being analyzed while a larger circle can represent a higher magnitude of the variable.  These circles can also be normalized which can make them easier to compare to each other.

In the map above, the amount of Walmarts in each state are represented with proportional circles.  Our eyes are first drawn to the biggest circle which is in texas, which tells us that the greatest amount of Walmart stores exists in this state.  There is also an overall spatial favoring of Wal-mart stores to exist in the eastern part of the U.S.  If these circles were normalized the differences would be even greater because the states in the West are significantly larger.  The only downside of these maps is that they are not necessarily good for determining small differences.  This is because it is, visually, hard to determine small differences between circles of approximately the same size.