This file consists of GeoJSON data generated by Mike Bostock from US Census data, and is in the public domain. This file used to be included in earlier versions of the D3 repository, and included this summary on its origins:
These are derived from the cartographic boundary files from the 2000 U.S. Census. Then, MapShaper was used to simplify the geometry, and ogr2ogr to convert the shapefiles to GeoJSON. Some additional work was done to preserve the FIPS codes, which are dropped from the shapefiles by MapShaper.
This file consists of data provided by the USDA, and is in the public domain. The values report agricultural productivty, by state, for 2004. Values are relative to an arbitrary baseline of the productivity of the state of Alabama in 1996 (1.0).
"Table 19. Indices of total factor productivity by State, 1960-2004" http://ers.usda.gov/data-products/agricultural-productivity-in-the-us.aspx
File derived from data provided by the United States Census Bureau, and integrated with geocoding data from: http://www.gpsvisualizer.com/geocoder/
"Table 1. Annual Estimates of the Resident Population for Incorporated Places Over 50,000, Ranked by July 1, 2011 Population: April 1, 2010 to July 1, 2011" http://www.census.gov/popest/data/cities/totals/2011/tables/SUB-EST2011-01.csv