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Q22: How accurate are the TIGER/Line coordinates?

The Census Bureau's mission to count and profile the Nation's people and
institutions does not require very high levels of positional accuracy in its
geographic products. Its files and maps are designed to show only the relative
positions of elements.

Coordinates in the TIGER/Line files have six implied decimal places. The
positional accuracy of these coordinates is not as great as the six decimal
places suggest. The positional accuracy varies with the source materials used,
but at best meets the established National Map Accuracy standards
(approximately +/- 167 feet) where 1:100,000-scale maps from the USGS are the
source. The Census Bureau can not specify the accuracy of feature updates
added by its field staff or of features derived from the GBF/DIME-Files or
other map sources. Thus, the level of positional accuracy in the TIGER/Line
files is not suitable for high-precision measurement applications such as
engineering problems, property transfers, or other uses that might require
highly accurate measurements of the earth's surface.

Despite the fact that TIGER/Line data positional accuracy is not as high as
the coordinate values imply, the six-decimal place precision is useful when
producing maps. This precision allows you to place features that are next to
each other on the ground in the correct position, relative to each other, on
the map without overlap.

We are in the beginning stages of a multi-year process to improve
the spatial accuracy of the features in the Census TIGER database and the
address information in the Master Address File (MAF). Currently, the Census
Bureau's Regional Office staff are updating address information based on
locally acquired sources. For more information about the MAF/TIGER Accuracy
Improvement Project, go to:

http://www.census.gov/geo/mod/maftiger.html

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