30. Continuously Variable Proportional Circle Map

http://www.neiu.edu/~ejhowens/377/examples.htm

Continuously variable proportional circle maps use circle to indicate to what degree phenomena occur in a given area. The circles come in all sizes on a continuous scale. The map above shows rent rates in the northeast U.S. in 1990. The larger the circle, the more expensive rent is. There are not set sizes for the circles and they do not necessarily indicate where exactly the rent rate occurs.