A ZIP Code is a system of postal codes used by the United States Postal Service (USPS) to simplify the distribution of mail. It is a 5-digit number that specifies an individual destination post office or mail delivery area. The term "ZIP" in ZIP Code stands for "Zone Improvement Plan". The basic format of a ZIP Code consists of five digits, and it was introduced on July 1, 1963. In 1983, an extended ZIP+4 code was introduced, which uses the basic five-digit code plus four additional digits for a full 9-digit ZIP Code.
ZIP Codes are numbered with the first digit representing a certain group of U.S. states, the second and third digits together representing a region in that group (or perhaps a large city), and the fourth and fifth digits representing a group of delivery addresses within that region. The main town in a region (if applicable) often gets the first ZIP Codes for that region; afterward, the numerical order often follows the alphabetical order. As of October 2019, there are 41,702 ZIP Codes in the United States.
ZIP Codes are used not only for tracking of mail but also commonly for gathering geographical statistics in the United States by some researchers. ZIP codes are not created for statistical analysis, thus use for statistical analysis is heavily criticized for numerous reasons and advised against as a cartographic practice. ZIP Code data is an integral part of dealer/store locator software on many websites, especially brick-and-click websites. This software processes a user-input ZIP Code and returns a list of store or business locations, usually in the order of increasing distance from the center of the input ZIP Code.
In summary, a ZIP Code is a 5-digit number that specifies an individual destination post office or mail delivery area used by the USPS to simplify the distribution of mail. It is numbered with the first digit representing a certain group of U.S. states, the second and third digits together representing a region in that group (or perhaps a large city), and the fourth and fifth digits representing a group of delivery addresses within that region.
