Flowingdata points out the right and wrong way to create proportionate circles, using a gaffe from Good to illustrate the point. You are supposed to size them to the AREA of the bubble (square root of the radius).

This is a nice followup to their tutorial last month on how to create bubble scatter diagrams in R (which also is a nice introduction to R if you’ve never played with it before.

For a more general discussion of bubble charts, try Junk Charts’ many critiques, or this article from Aventine Partners: “Bubble Charts, Good or Bad?”