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Q16: Does the ZIP Code file you have available for downloading contain a
complete and up-to-date list of ZIP Codes?

The ZIP file doesn't include all ZIP Codes because it was based only on those
areas for which we had city-style addresses (which leaves out a lot of rural
areas). The file was created as a byproduct of another operation (a data
product based on the ZIP codes we collected with the 1990 Census data). For
this Census data product, we took advantage of the fact that we had some
ZIP Code data as a consequence of trying to collect addresses for the Census
questionnaire mailout so we published data for those ZIP Codes. This ZIP
internal point file is basically the lat/long for the ZIP Codes in that product.
We put it on the Web in case anyone found it useful. It was not intended to
be an authoritative source on ZIP Codes.

Note that the task of creating a lat/long or polygon file of all ZIP Codes is
not as easy as it seems since ZIP Codes are not designed to be polygons and
can't easily be forced into them - particularly in rural areas. To our knowledge
there are no official internal point or polygon files available. However, because
of the demand for ZIP Code data and maps, the Census Bureau, for Census 2000,
created a new statistical area called the ZIP Code Tabulation Area (ZCTA).
ZCTAs are close area approximations of U.S. Postal Service ZIP Codes and
were designed to overcome the difficulties of defining clear boundaries to which
data could be attached. For more information on ZCTAs go to:

http://www.census.gov/geo/ZCTA/zcta.html

For more information on ZIP Codes the U.S. Postal Service site may be of interest:

http://www.usps.gov

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Next: Q17: Does the Census Bureau produce ZIP Code maps?
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