ZIP Code Tabulation Areas (ZCTAs) are generalized representations of United States Postal Service (USPS) ZIP Code service areas.

The USPS ZIP Codes identify the individual post office or metropolitan area delivery station associated with mailing addresses. USPS ZIP Codes are not areal features but a collection of mail delivery routes.

ZIP Code Tabulation Areas (ZCTAs)ZIP Code Tabulation Areas (ZCTAs) are generalized areal representations of United States Postal Service (USPS) ZIP Code service areas.The USPS ZIP Codes identify the individual post office or metropolitan area delivery station associated with mailing addresses. USPS ZIP Codes are not areal features but a collection of mail delivery routes.The term ZCTA was created to differentiate between this entity and true USPS ZIP Codes. ZCTA is a trademark of the U.S. Census Bureau; ZIP Code is a trademark of the U.S. Postal Service.How ZCTAs are CreatedThe Census Bureau first examined all of the addresses within each census block to define the list of ZIP Codes by block. Next, the most frequently occurring ZIP Code within each block was assigned to the entire census block as a preliminary ZCTA code. After all of the census blocks with addresses were assigned a preliminary ZCTA code, blocks were aggregated by code to create larger areas.The Census Bureau assigned blocks that contained addresses, but did not have a single most frequently occurring ZIP Code to the ZCTA with which the blocks had the longest shared boundary.If the area of an unassigned enclave was less than two square miles, it was assigned to the surrounding ZCTA. The Census Bureau used block group boundaries to identify and group unassigned blocks. These unassigned blocks were merged into an adjacent ZCTA based on the length of shared boundary.For the Census 2000 ZCTAs the Census Bureau created ZCTAs that ended in "XX" to represent large areas of land without ZIP Codes or "HH" to represent large areas of water without ZIP Codes. For the 2010 Census, large water bodies and large unpopulated land areas do not have ZCTAs.ZCTAs were created using residential and nonresidential ZIP Codes that are available in the Census Bureau’s MAF/TIGER database. ZIP Codes assigned to businesses only or single delivery point address will not necessarily appear as ZCTAs.In most instances the ZCTA code is the same as the ZIP Code for an area.In creating ZCTAs, the Census Bureau took the most frequently occurring ZIP Code in an area for the ZCTA code. Some addresses will end up with a ZCTA code different from their ZIP Code.Some ZIP Codes represent very few addresses (sometimes only one) and therefore will not appear in the ZCTA universe.Key Differences between Census 2000 and 2010 Census ZCTAsCensus 2000Includes the U.S. and Puerto RicoCover the full extent of the nation - "wall-to-wall" coverage3-digit and 5-digit ZCTA's available"XX" suffix used to represent large land areas such as national parks"HH" suffix used to represent large water bodies2010 CensusIncludes the U.S., Puerto Rico, and the Island AreasDo not cover the full extent of the nation - "holes" exist5-digit ZCTA's only"XX" retired - Large land areas such as national parks do not have ZCTA coverage"HH" retired - Large water bodies do not have ZCTA coverage