That is why I suggest the FPIS code, over the  ZCTA code.

The FPIS code for a place is used by the U.S. Board on Geographic Names (http://geonames.usgs.gov/index.html) and can...

Before you use a Zipcode a key, consider using the FIPS code

http://www.census.gov/geo/www/fips/fips.html

http://www.census.gov/geo/www/tiger/zip1999.html

Census stopped using them as a "key" becuse they change too much.

See here

http://www.census.gov/popest/geographic/codes02.html

For my project, which...