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What did ZIP + 4 codes add to the original ZIP Code system?
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postal system
A United States Postal Service worker retrieving mail from a mailbox in Manheim, Pennsylvania.
Introduced by the U.S. Postal Service in 1983, the ZIP + 4 code system was designed to further increase the efficiency of automated mail sorting operations.12
While the original five-digit ZIP Code identified a general post office or delivery zone, the four additional digits provide a much more granular geographic designation. Specifically:13
- The first two extra digits identify a specific sector, such as a cluster of large buildings or a group of streets.1
- The last two extra digits represent a precise segment, which may consist of a single floor in an office building, one side of a city block, or a specific group of post office boxes.12
By narrowing the destination to such a specific level, the system allows automated equipment to sort mail more effectively, often down to the level of individual delivery routes or specific business departments.23