The Census Bureau makes changes to geographic boundaries over time, especially for smaller units of description. Geolytics has standardized these geographies so that the characteristics of small areas can be compared from 1970 to 2000 at the tract level.
Years: 1970, 1980, 1990, 2000
Geographies: Nation, State, County, Tract.
Formats: Comma-separated values (CSV), Database file (DBF), MapInfo file (MID/MIF), and Shapefile (SHP).
Notes: Only works with Internet Explorer. Census data with details such as population, household, and housing characteristics, income, poverty status, education level, employment, housing costs, immigration, and other variables.
Geographies: Nation, State, County, ZIP code, Census Tract 1910-2000, Census Block-group 1990 & 2000, and others which vary by year.
Formats: Comma-separated values (CSV) and Shapefile in compressed (zipped) format (ZIP).
Notes: You must register with NHGIS (for free) to download data from the site. NHGIS offers the following options to obtain data:
Years: Samples from fifteen federal censuses (1850-2000) and the American Community Surveys (2000-2006).
Geographies: Public use microdata areas
Formats: Can be downloaded with syntax files for SAS, SPSS, Stata
Notes: These are microdata, as distinct from the aggregate (published) data found in nearly every other census data resource. See What are microdata? for details.
Geographies: Nations, regions, states, counties, metropolitan areas, largest cities, coastal regions, places
Formats: PDF, HTML
Notes: Information is easy to scan by time period and geography, but is only a subset of the Census Bureau's Decennial Census of Population and Housing Reports.