This choropleth encodes unemployment rates from 2008 with a quantize scale ranging from 0 to 15%. A threshold scale is a useful alternative for coloring arbitrary ranges.
This is a modification of Mike Bostock's example, so single out individual states, picked out using their FIPS code. The State outlines can be also be found on GitHubt @ https://gist.github.com/4090846. A Bottle sever is included, for viewing at home.