System of postal-zone codes (zip stands for zone improvement plan) introduced in the U.S. in 1963 to improve mail delivery and exploit electronic reading and sorting capabilities. The original code, which corresponds to the postal codes used in most countries in the world, consists of five numbers. The first three identify the state and portion of the state, the last two a specific post office or zone. In 1983 a nine-digit code (created by adding a hyphen and four digits) was introduced to further speed delivery; the first two added digits specify a particular sector, the last two an even smaller segment (e.g., one side of a city block, or a single floor in a large building).
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