Environmental Summaries 2006
IPUMS NHGIS environmental summaries provide land cover data summarized over counties and census tracts.
Social Explorer; Steven Manson, Jonathan Schroeder, David Van Riper, and Steven Ruggles. IPUMS National Historical Geographic Information System: Version 12.0 [Database]. Minneapolis: University of Minnesota. 2017. http://doi.org/10.18128/D050.V12.0