Range Graded Proportional Circle Map

This map was taken from http://www.e-cartouche.ch/content_reg/cartouche/cartdesign/en/html/ThemMaps_ThemData.html

This is a good example of a Range Graded Proportional Circle Map.  These maps use circles to show different ranges of data.  Instead of using exact sizes for circles, it uses a variance of size.  In this case it shows inhabitants of the communes in the area of Zurich, Switzerland.