This is just one of a number of maps prepared by a trio at U of Michigan (physics and complex systems). Their page describes the methods used to prepare each. The cartogram (above) is based on a geographical map that uses the color scaling proposed by Robert Vanderbei at Princeton. We had alreday come across Vanderbiei's work in an earlier discussion of voting maps that JC
and MC MasterChef had brought to our attention.
My favorite of the Vanderbei maps, from an aesthetic standpoint if nothing else, overlays the colors on a map that includes mountains. Both striking and informative.
The Princeton page has some information on voting predictions as well.
By popular demand, the Michigan site is making the purple cartogram (above) and its companion map available as wallpaper.

The first afoe European weblog awards