The mating of maps with statistics goes back to this 1826 graphic by mathematician Charles Dupin that illustrated the extent of illiteracy in France via regional shadings.  Later these thematic plots came to be known as a “choropleth”—from the Greek for region (choro) and multitude (pleth).  I only heard of this term this week, thanks to a Flowing Data blog by Nathan Yau with a tip on how to produce choropleth maps online.

Another variation on thematic maps is the “cartogram”—for example this one published yesterday by the Wall Street Journal that illustrates American unemployment.  A cartogram shifts shapes so their areas correlate to some measure, in this case the relative density and number of workers.  I am pleased to see on the last of the three figures that my home state of Minnesota fared well with its recovery from the Great Recession.  However, I don’t like seeing our outline distorted so.  The Dakotas and neighboring states really got squeezed.  Perhaps we get some oil out of it to make our economy even better. ; )