GIS Boundary Files

NHGIS boundary files are derived primarily from the U.S. Census Bureau's TIGER/Line files.

For 1990 and 2000 areas, NHGIS modified the 2000 TIGER/Line definitions only by erasing coastal water areas. Because the 2000 TIGER/Line files contain no identifiers for census areas from 1980 and earlier, NHGIS researchers obtained boundary definitions for those years by consulting other sources, including 1992 TIGER/Line data for 1980 census tracts; maps from printed census reports for 1910-1980 census tracts and other small areas; and the Map Guide to the U.S. Federal Censuses, 1790-1920, by William Thorndale and William Dollarhide (Genealogical Publishing Co., Baltimore, MD, 1987), for counties and states back to 1790. Where the historical boundaries follow 2000 TIGER/Line features, the original NHGIS boundary files re-use those TIGER/Line features. Elsewhere, NHGIS researchers digitized new boundaries. NHGIS boundary files based on these files are identified as "2000 TIGER/Line +" in the Basis column found in the Select Data grid.

2000 boundaries are also available in a format derived from the U.S. Census Bureau's 2010 TIGER/Line files. NHGIS modified the TIGER/Line definitions only by erasing 2010 coastal water areas. NHGIS boundary files based on these files are identified as "2010 TIGER/Line +" in the Basis column found in the Select Data grid. These 2000 files derived from 2010 TIGER/Line will better align with 2010 and newer GIS boundary files.

2010 boundaries are derived from the U.S. Census Bureau's 2010 TIGER/Line files. NHGIS modified the TIGER/Line definitions only by erasing coastal water areas. NHGIS boundary files based on these files are identified as "2010 TIGER/Line +" in the Basis column found in the Select Data grid. 

2011 boundaries are derived from the U.S. Census Bureau's 2011 TIGER/Line files. NHGIS modified the TIGER/Line definitions only by erasing coastal water areas. NHGIS boundary files based on these files are identified as "2011 TIGER/Line +" in the Basis column found in the Select Data grid. 

2012 boundaries are derived from the U.S. Census Bureau's 2012 TIGER/Line files. NHGIS modified the TIGER/Line definitions only by erasing coastal water areas. NHGIS boundary files based on these files are identified as "2012 TIGER/Line +" in the Basis column found in the Select Data grid.

The 2013 113th Congressional District boundaries are derived from the U.S. Census Bureau's 113th Congressional District TIGER/Line files. NHGIS modified the TIGER/Line definitions only by erasing coastal water areas using the 2012 TIGER/Line coastal water definitions. NHGIS boundary files based on these files are identified as "113th Congressional District TIGER/Line +" in the Basis column found in the Select Data grid.  

1980 boundaries for Places and County Subdivisions are derived from the U.S. Census Bureau's 1992 TIGER/Line files. NHGIS modified the TIGER/Line definitions only by erasing coastal water areas using the 2000 TIGER/Line coastal water definitions. NHGIS boundary files based on these files are identified as "1992 TIGER/Line +" in the Basis column found in the Select Data grid.

Because the Census Bureau has regularly made accuracy improvements to TIGER/Line features between releases, boundaries derived from different TIGER/Line releases are not consistently comparable with each other. 

Realigned GIS Boundary Files

Because the Census Bureau made major accuracy improvements to TIGER/Line features between the 2000 and 2008 TIGER/Line releases, the original NHGIS shapefiles based on 2000 TIGER/Line features are not comparable with newer TIGER/Line data. We therefore generated new 2008-based boundary files by systematically realigning the boundaries for tracts and counties to fit with 2008 TIGER/Line features. The realigned NHGIS boundary files are identified as "2008 TIGER/Line +" in the Basis column found in the Select Data grid.

The Census Bureau made additional improvements to TIGER/Line features after 2008, so the 2008 TIGER/Line-based files are not consistently comparable with 2010 and later TIGER/Line files. In general, most 2008-based boundaries align better than 2000-based boundaries with 2010 and later TIGER/Line files, but the 2008-based boundaries also include occasional gross inaccuracies.

For users who have no need to compare historical boundaries with boundaries from 2010 or later, we recommend using the original 2000-based NHGIS boundary files. For users who do wish to compare or overlay historical boundaries with boundaries from 2010 or later, we recommend downloading and examining both the 2000- and 2008-based versions of historical boundaries in order to determine which is more suitable for your study area and analysis.  For users who wish to overlay 2000 boundaries with boundaries from 2010 or later, we recommend using the 2000 boundaries derived from 2010 TIGER/Line.

Census Bureau TIGER/Line Documentation

1992 TIGER/Line (PDF) (2MB)

2000 TIGER/Line (PDF) (1MB)

2008 TIGER/Line (PDF) (2MB) 

2010 TIGER/Line (PDF) (4MB)

2011 TIGER/Line (PDF) (4MB)

2012 TIGER/Line (PDF) (4MB)

113th Congressional District (2013) TIGER/Line (PDF) (3MB)