ZIP Code Tabulation Areas (ZCTAs™) are a statistical entity initially developed by the U.S. Census Bureau for tabulating summary statistics from census data. This entity was developed for Census 2000 to overcome the difficulties in precisely defining the land area covered by each ZIP Code®. Current 2010 Census ZCTA boundaries, data, and information can be found here: 2010 Census ZCTAs.
ZCTAs are generalized area representations of U.S. Postal Service (USPS) ZIP Code service areas. For Census 2000, each ZCTA was built by aggregating the Census 2000 blocks, whose addresses use a given ZIP Code. ZCTAs represent the most frequently occurring USPS five-digit ZIP Code found in the given area. For Census 2000, those areas where it was difficult to determine the prevailing five-digit ZIP Code, the higher-level three-digit ZIP Code was used for the ZCTA code. For more information, please refer to the ZCTA (FAQ) Frequently Asked Questions Web page.