Weekly blog map #7: Proportional Symbol

I want you to track down an interesting proportional symbol (or graduated symbol map). It is a map that uses one symbol of varying size to illustrate magnitude differences. The most common variety uses circles, but squares, triangles, coffee cups, beers....just about anything can be made to fit. 

Find one, post it on your blog, and tell us why you found it interesting!

Here is a nice example from the Washington Post: