Coverage of the LTDB

Note that not all areas of the U.S. were tracted in 1970. In addition, some tracts are missing for the following reasons.

2000 to 2010 crosswalk

There are 269 tracts that are in 2000 SF1, but not in our crosswalk. This is because they have zero population in 2000. Since we use 2000 block population to generate the interpolation weights, 2010 tracts that are comprised entirely of unpopulated 2000 tracts were omitted. This also affects the crosswalks from earlier years because we first interpolate to 2000 boundaries and then to 2010 boundaries.

1990 to 2010 crosswalk

There are 381 tracts that are in 1990 STF1, but not in our crosswalk:

• 100 had zero population in 1980 so they were not interpolated
• 253 are populated only by crews of vessels
• 28 are omitted because they had zero population in 2000

1980 to 2010 crosswalk

In 1980, valid tract numbers range from 0001 to 9899.99. Greater numbers indicate block numbering areas (BNAs) that are in untracted areas. We did not interpolate the 3,507 BNAs in untracted areas.

There are 360 tracts in 1980 STF1 that are not in our crosswalk:

• 138 had zero population in 1980 so they were not interpolated
• 199 are populated only by crews of vessels
• 23 are omitted because they had zero population in 2000

1970 to 2010 crosswalk

There are 278 tracts in 1970 Fourth Count File A that are not in our crosswalk:

• 67 had zero population in 1970 so they were not interpolated.
• 186 are populated only by crews of vessels
• 17 are omitted because they had zero population in 2000
• 8 are omitted because they are not in the NHGIS shapefile