For instance, a single ZIP code is used for all US Navy mail. However, some ZIP codes have nothing to do with geogaphic areas. In most cases, addresses in close proximity to each other are grouped in the same ZIP code which gives the appearance that ZIP codes are defined byĪ clear geographic boundary.

Some ZIP codes will span multiple states in order to make mail routing and delivery more efficient. They are intended to group mail to allow the USPS to deliver mail This method isn't a universal rule though so the ZIP+4 must still be looked up for each POĭespite the fact that ZIP codes seem to be geographic in nature, that wasn't their intended purpose. The same ZIP+4 code by using the last several digits of the PO Box number. Sometimes, several PO Box numbers are grouped into It is also common for each PO Box number to correspond to a unique ZIP+4 code. A ZIP+4 code may correspond to a city block, group of apartments, orĪn individual high-volume receiver. The ZIP+4 code is not required, but it aids the post office in additional sorting of mail. It's easy to follow the gradient across each of the zonesĮven though there are a few exceptions (such as the southwest tip of Georgia which uses 39XXX like central Mississippi). In the map, 0 is closer to white and 9 is much more vivid. Map of the first 3 digits of zip codes, the digits after the first are also The sec centers are not open to the public and usually do most sorting overnight. All mail with the same first 3 digits is first delivered to the same sec center where it is sorted according to the last 2 digits and distributed to The first 3 digits of a ZIP code determine the central mail processing facility, also called sectional center facility or 'sec center', that is used to process and They are assigned in order from the north east to the west coast. The map of the first digit of zip codes above shows The first digit of a USA ZIP code generally represents a group of U.S. 22313 for the PO Boxes of Alexandria, VA) Unique/single high volume address (ex.Sorting packages and calculating the time and cost of shipping a package (the shipping rate). Though ZIP codes were originally developedįor USPS, many other shipping companies such as United Parcel Service (UPS), Federal Express (FedEx), DHL, and others make use of ZIP codes for The additional 4 digits help USPS more precisely group mail for delivery. The basic 5-digit format was first introduced in 1963 and laterĮxtended to add an additional 4 digits after a dash to form a The term ZIP stands for Zone Improvement Plan. Some still refer to ZIP codes as US postal codes. ZIP codes near me are shown on the map above. US ZIP codes are a type of postal code used within the United States to help the United States Postal Service (USPS) route mail more efficiently.

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