Documentation for the digital sources of NHGIS tabular data:
- Secondary Sources (1790-1972)
- Decennial Census Summary Files (1960-2010)
- County Business Patterns (1970-2003)
- American Community Survey (2009-2016)
Time series tables link together comparable statistics from multiple censuses. The documentation describes how time series are constructed; summarizes which topics, years, and areas are covered; and provides a listing of all table sources and notes.
The GIS files are mainly based on the U.S. Census Bureau TIGER/Line files with additional editing and digitization to produce historical boundaries in accordance with several map sources.
Two types of releases are documented: updates to the NHGIS website and updates to the NHGIS data (tabular or boundary data).