This map shows unemployment data for census tracts in San Mateo county, California, from 2010.
The idea for doing this was inspired by the San Mateo Hackathon. The data comes from County of San Mateo Open Data Portal. Census tract shapes originally downloaded from US Census 2010 TIGER/LineĀ® Shapefiles: Census Tracts then simplified using MapShaper.
Draws from the D3 Choropleth Example.