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Small towns often don't have street delivery everything for a ZIP code might go to post office boxes at one location. Since all addresses for a ZIP will be served by a single post office, it's tempting to start with that office's city boundary as the encompassing border for all ZIP codes served by that office, but exceptions occur: for example, a post office will serve ZIP codes outside the city, such as in unincorporated towns. The Zip +4 adds four more numbers, which are used by USPS to identify one side of a block or a single building with multiple occupants, or post office boxes. The basic USA Zip Code format consists of five numerical digits. The ZIP stands for Zone Improvement Plan and it is used for efficient mail travel when sender uses a code in the postal address.
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It might mean computing the minimum rectangular bounding box enclosing all the addresses in a ZIP, or using a Graham scan to compute a "tighter" polygon, or using Lloyd's algorithm to polygonize a map, but how to choose the "best" boundary isn't always clear as shown in these 3 different boundaries for 5 points. The USA ZIP code is the postal code system used by the United States Postal Service (USPS). Addresses along the route are visited in a specific order, however there is no guarantee what path is taken by the mail carrier between two points along the route, so attempts at plotting routes as lines (or plotting all routes in a ZIP as a collection of lines) can't always be accurate.īecause ZIP codes are collections of points, the concept of "boundary" is ambiguous. Cheap sources of current data are vendors like Semaphore Corporation.Īddresses within a ZIP code are assigned to numbered delivery routes. The USPS is the sole determiner of what ZIP code is assigned to what address, so they are the best source of current and correct data, which changes monthly. A five-digit ZIP code covers an arbitrary collection of delivery points (addresses).