zipCode

A ZIP code is a postal code used by the United States Postal Service (USPS) to identify locations for mail delivery. The term stands for Zone Improvement Plan and the system was introduced in 1963 to improve sorting and delivery efficiency. The basic form is a five-digit code.

The first digit of a ZIP code denotes a broad geographic area of the United States, the next two digits designate a regional area or sectional center facility, and the last two digits identify a more specific post office or delivery area. In addition to the five-digit form, a ZIP+4 code adds a hyphen followed by four more digits, introduced in 1983, to further refine routing to a smaller segment such as a block, building, or set of apartments.

ZIP codes are used primarily for mail routing and address sorting by the USPS, but they also serve as a convenient geographic identifier in business, government, and research. They support address validation, logistics planning, and geographic analysis. The United States Census Bureau creates ZIP Code Tabulation Areas (ZCTAs) to present statistical data approximating ZIP code geography, since ZIP codes themselves are not designed as exact political or administrative boundaries. A single ZIP code can cover multiple communities, and conversely a community may span several ZIP codes.

Beyond the continental United States, ZIP codes are also used for U.S. territories and for military mail via APO/FPO addresses, which route through specialized facilities. While widely used as a proxy for location, ZIP codes should not be presumed to align precisely with city or county boundaries, and boundaries can change over time as the postal system evolves.