АҚШ пошта индексі және ZIP+4 коды

Numeric postal code used in the US and its territories

A ZIP Code (an acronym for Zone Improvement Plan) is a system of postal codes used by the United States Postal Service (USPS). The term ZIP was chosen to suggest that the mail travels more efficiently and quickly (zipping along) when senders use the code in the postal address. Introduced on July 1, 1963, the basic format comprised five digits. In 1983, an extended code was introduced named ZIP+4 ; it included the five digits of the ZIP Code, followed by a hyphen and four digits that designated a more specific location. ZIP Code and ZIP+4 are registered trademarks of the United States Postal Service, which also registered ZIP Code as a service mark until 1997.

In 1983, the U. S. Postal Service introduced an expanded ZIP Code system that it named ZIP+4, often known as "plus four codes", "add on codes", or "add ons". A ZIP+4 Code uses the basic five digit code plus four additional digits to identify a geographic segment within the five digit delivery area, such as a city block, a group of apartments, an individual high volume receiver of mail, a post office box, or any other unit that could use an extra identifier to aid in efficient mail sorting and delivery. However, the new format was not adopted universally by the public; it eventually became obsolete with modern technology. In general, mail is read by a multiline optical character reader (MLOCR) that almost instantly determines the correct ZIP+4 Code from the address—along with the even more specific delivery point—and sprays an Intelligent Mail barcode (IMb) on the face of the mail piece that corresponds to 11 digits—nine for the ZIP+4 Code and two for the delivery point. For post office boxes, the general but not invariable rule is that each box has its own ZIP+4 Code. The add on code is often one of the following: the last four digits of the box number (e. g. PO Box 107050, Albany, NY 12201 7050), zero plus the last three digits of the box number (e. g., PO Box 17727, Eagle River, AK 99577 0727), or, if the box number consists of fewer than four digits, enough zeros are attached to the front of the box number to produce a four digit number (e. g., PO Box 77, Juneau, AK 99750 0077). However, there is no uniform rule, so the ZIP+4 Code must be looked up individually for each box (e. g. using the USPS's official ZIP Code Lookup tool, and being sure to enter just city and state, not the 5 digit ZIP).

The ZIP Code is often translated into an Intelligent Mail barcode that is printed on the mailpiece to make it easier for automated machines to sort. A barcode can be printed by the sender (some word processing programs such as WordPerfect include the feature), but this is not recommended, as the address to ZIP lookup tables can be significantly out of date. Customers who send bulk mail can get a discount on postage if they have printed the barcode themselves and have presorted the mail. This requires more than just a simple font; mailing lists must be standardized with up to date Coding Accuracy Support System (CASS) certified software that adds and verifies a full, correct ZIP+4 Code and an additional two digits representing the exact delivery point. Furthermore, mail must be sorted in a specific manner to an 11 digit code with at least 150 mailpieces for each qualifying ZIP Code and must be accompanied by documentation confirming this. These steps are usually done with PAVE certified software that also prints the barcoded address labels and the barcoded sack or tray tags. The assignment of delivery point digits (the 10th and 11th digits) is intended to ensure that every single mailable point in the country has its own 11 digit number. The delivery point digits are calculated based on the primary or secondary number of the address. The USPS publishes the rules for calculating the delivery point in a document called the CASS Technical Guide.

The second and third digits represent the sectional center facility (SCF) (e. g. 477xx = Vanderburgh County, Indiana), and the fourth and fifth digits represent the area of the city (if in a metropolitan area), or a village/town (outside metro areas), e. g. 47722 (4=Indiana, 77=Vanderburgh County, 22=University of Evansville area). When a sectional center facility's area crosses state lines, that facility is assigned separate three digit prefixes for the states that it serves. In some urban areas, like 462 for Marion County, Indiana, the three digit prefix will often exist in one county, while, in rural and most suburban areas, the prefix will exist in multiple counties; for example, the neighboring 476 prefix is found in part or entirely in six counties: Gibson, Pike, Posey, Spencer, Vanderburgh, and Warrick. In some cases, an urban county may have more than one prefix. This is the case with Allen (467, 468), Lake (464, 463), St. Joseph (465, 466), and Vanderburgh (476, 477) counties. Cities like Chicago, Houston, Los Angeles, and New York City have multiple prefixes within their city limits. In some cases, these may be served from the same SCF, such as in San Diego County, California, where the three digit prefixes 919 and 920 are used for suburban and rural communities, and 921 for the city of San Diego itself, although all three are processed through the same SCF. Despite the geographic derivation of most ZIP Codes, the codes themselves do not represent geographic regions; in general, they correspond to address groups or delivery routes. As a consequence, ZIP Code "areas" can overlap, be subsets of each other, or be artificial constructs with no geographic area (such as 095 for mail to the Navy, which is not geographically fixed). In similar fashion, in areas without regular postal routes (rural route areas) or no mail delivery (undeveloped areas), ZIP Codes are not assigned or are based on sparse delivery routes, and hence the boundary between ZIP Code areas is undefined. For example, some residents in or near Haubstadt, Indiana, which has the ZIP Code 47639, have mailing addresses with 47648, the ZIP Code for neighboring Fort Branch, Indiana, while others living in or near Fort Branch have addresses with 47639. Many rural counties have similar logistical inconsistencies caused by the aforementioned sparse delivery routes, often known as Rural Routes or by some other similar designation.

Like area codes, ZIP Codes are sometimes divided and changed, especially when a rural area becomes suburban. Typically, the new codes become effective once announced, and a grace period (e. g., one year) is provided in which the new and old codes are used concurrently so that postal patrons in the affected area can notify correspondents, order new stationery, etc. In rapidly growing communities, it is sometimes necessary to open a new sectional center facility, which must then be allocated its own three digit ZIP code prefix or prefixes. Such allocation can be done in various ways. For example, when a new sectional center facility was opened at Dulles Airport in Virginia, the prefix 201 was allocated to that facility; therefore, for all post offices to be served by that sectional center facility the ZIP Code changed from an old code beginning with 220 or 221 to a new code or codes beginning with 201. However, when a new sectional center facility was opened to serve Montgomery County, Maryland, no new prefix was assigned. Instead, ZIP Codes in the 207 and 208 ranges, which had previously been assigned alphabetically, were reshuffled so that 207xx ZIP Codes in the county was changed to 208xx codes, while 208xx codes outside that county were changed to 207xx codes. Because Silver Spring (whose postal area includes Wheaton) has its own prefix, 209, there was no need to apply the reshuffling to Silver Spring; instead, all mail going to 209xx ZIP Codes was simply rerouted to the new sectional center facility. On the other hand, depopulation may cause a post office to close and its associated ZIP Code to be deallocated. For example, Centralia, Pennsylvania's ZIP Code, 17927, was retired in 2002, and ZIP Codes for Onoville (14764), Quaker Bridge (14771) and Red House (14773) in New York were prevented from going into use in 1964 in preparation for the Kinzua Dam's completion.

Delivery services other than the USPS, such as FedEx, United Parcel Service, and DHL, require a ZIP Code for optimal internal routing of a package.

as of October 2019, there are 41,702 ZIP Codes in the United States. Due to convenience, ZIP Codes are used not only for tracking of mail, but also commonly for gathering geographical statistics in the United States by some researchers. ZIP Codes are not created for statistical analysis, thus use for statistical analysis is heavily criticized for numerous reasons and advised against as a cartographic practice. As ZIP Codes are not polygons, but collections of mail routes and points, they are unsuitable for publication or distribution of most data. Polygons for ZIP Codes are not released by the USPS and instead interpolated by 3rd party vendors.

ZIP Codes may not currently be used to identify existing legislative districts. Although the website of the United States House of Representatives has a "Find Your Representative" feature that looks up congressional districts based on ZIP Codes alone, it often returns multiple districts corresponding to a single ZIP Code. This is because different parts of one ZIP Code can be in different districts. One proposal to eliminate the possibility of extreme partisan gerrymandering calls on using ZIP Codes as the basic units for redistricting.

A 1978 proposal for a nationwide system of community networks suggested using ZIP Codes for routing. ZIP Code data is an integral part of dealer / store locator software on many websites, especially brick and click websites. This software processes a user input ZIP Code and returns a list of store or business locations, usually in the order of increasing distance from the center of the input ZIP Code. As the ZIP Code system is confined to the U. S. Postal network, websites that require ZIP Codes cannot register customers outside the United States. Many sites will purchase postal code data of other countries or make allowances in cases where the ZIP Code is not recognized. ZIP Codes are regularly used on the Internet to provide a location in situations where an exact address is not necessary (or desirable) but the user's municipality or general location is needed. Examples (in addition to the store locator example listed above) include weather forecasts, television listings, local news, and online dating (most general purpose sites, by default, search within a specified radius of a given ZIP Code, based on other users' entered ZIP Codes).

ZIP Codes are used in credit card authorization, specifically Address Verification System (AVS). When a merchant collects the entire address, the ZIP Code is an important part of AVS. In some cases, the ZIP Code is the only thing used for AVS, specifically where collecting a signature, or other information is infeasible, such as pay at the pump or vending machines.