is a postal code
used by the US Postal Service
. It is a 5-digit number that identifies a specific geographic delivery
area. It was established in 1963 to replace the aging
and limited Zone system. Hence, ZIP
stands for "Zone Improvement Plan
Considering 80521 -- a zip code for Colorado State University:
- The first three digits identify which central postal sorting station. So the 805 zone includes both post offices in Ft. Collins, plus a number of smaller surrounding towns.
- The second two digits, 21, designate an associate post office, post office branch, or post office station. In this case, 21 is assigned to the North Fort Collins Station. All post offices are assigned at least one unique 5-digit code, and often many more.
ZIP Codes can represent an area within a state (an area that may or may not cross county boundaries), an area that crosses state boundaries (an unusual condition), or a single building or company that has a very high mail volume. For example, the firstname.lastname@example.org reports that the President and his/her family have the ZIP-code 20500. Smokey the Bear is the only person(?) in Zip Code 20252. The entire Sears Tower in Chicago is at 60684. In general, Zip codes start at 00000 in the Eastern US, and enter the 90000s as they go west. Hawaii and Alaska have Zip codes in the 90000 rage.
ZIP+4 is an enhanced code consisting of the 5-digit ZIP Code and four additional digits that identify a specific range of delivery addresses. The first two additional
digits designate the sector (a geographic area) and the last two digits designate the segment (a building, floor, etc.).
ZIP Code and Zip+4 are USPS trademarks.
The POSTNET barcode found printed on nearly all mail contains at minimum the ZIP code, and at maximum your ZIP+4 code, and the last two digits of your house number. A mod-10 checkdigit is at the end.
A fair amount of this is sourced direct from USPS documents, so it is a little dry.