This choropleth displays unemployment rates by US county in 2012 (annual averages).
This sample tries to show how to use JSON-stat in combination with D3. The code has been directly copied and lightly adapted from the original Mike Bostock's Choropleth to retrieve JSON-stat data. The TopoJSON file (us-counties.json) has been normalized to use 5-digit strings as ids (instead of numbers).
It is not particularly fast: 4 libraries and two big JSON files (map and data) are used.
Data source: Bureau of Labor Statistics.