The ZIP Code system (an acronym for Zone Improvement Plan) is the 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 include the code in the postal address. ZIP+4 is a registered trademark of the United States Postal Service, which also registered ZIP Code as a service mark until 1997, and which claims "ZIP Code" as a trademark though it is not registered.
Introduced on July 2, 1963, the basic format was five digits, the first designating a region of the country and subsequent digits localizing the destination further. 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 location even more specific than the original five.
Private carriers and the USPS use ZIP Codes to route deliveries. In addition, ZIP Codes have become a basis for breaking down demographic, marketing, and sales data for analytical purposes.
History Early postal zones
The early history and context of postal codes began with postal district/zone numbers. The United States Post Office Department (USPOD) implemented postal zones for 124 large cities in May 1943. Postmaster General Frank C. Walker explained that many experienced postal clerks were going into the army, and the zone system would enable inexperienced clerks to sort mail without having to learn the delivery area of each city carrier.
For example:
The "16" is the number of the postal zone in a specific city.
Establishment By the early 1960s, a more organized system was needed. Robert A. Moon, who is considered the father of the ZIP Code, proposed it in 1944 while working as a postal inspector.Bullamore, Tim (2001). Robert Moon Obituary. Retrieved from https://www.independent.co.uk/news/obituaries/robert-moon-729034.html . Non-mandatory five-digit ZIP Codes were introduced nationwide on July 1, 1963, and less than three months later Moon estimated that there were already ZIP Codes on as much as 30% of mail. The USPOD issued its Publication 59: Abbreviations for Use with ZIP Code on October 1, 1963, with the list of two-letter state abbreviations which are generally written with both letters capitalized."State Abbreviations", USPS.com . An earlier list, publicized in June 1963, had proposed capitalized abbreviations ranging from two to five letters. According to Publication 59, the two-letter standard was "based on a maximum 23-position line, because this has been found to be the most universally acceptable line capacity basis for major addressing systems", which would be exceeded by a long city name combined with a multi-letter state abbreviation, such as "Sacramento, Calif." along with the ZIP Code. The abbreviations have remained unchanged, except for Nebraska, which was changed from NB to NE in 1969 at the request of the Canadian Post Office, to avoid confusion with New Brunswick.
The phrase "zone improvement plan" is credited to D. Jamison Cain, a Postal Service executive. The post office credits Moon with only the first three digits of the ZIP Code, which describe the sectional center facility (SCF) or "sec center". An SCF is a central mail processing facility with those three digits. The fourth and fifth digits, which give a more precise locale within the SCF, were proposed by Henry Bentley Hahn Sr.
The SCF sorts mail to all post offices with those first three digits in their ZIP Codes. The mail is sorted according to the final two digits of the ZIP Code and sent to the corresponding post offices in the early morning. Sectional centers do not deliver mail and are not open to the public, although the building may include a post office that is open to the public, and most of their employees work the night shift. Items of mail picked up at post offices are sent to their SCFs in the afternoon, where the mail is sorted overnight. In the case of large cities, the last two digits as assigned generally coincided with the older postal zone number.
For example:
In 1967, these became mandatory for second- and third-class bulk mailers, and the system was soon adopted generally. The United States Post Office used a cartoon character, which it called Mr. ZIP, to promote the use of the ZIP Code. The name "Mr. ZIP" was coined by D. Jamison Cain. Mr. ZIP was often depicted with a legend such as "USE ZIP CODE" in the selvage of panes of postage stamps or on the covers of booklet panes of stamps. Mr. ZIP was featured prominently alongside musical group "The Swingin' Six" in a variety show that the post office used to explain the importance of using ZIP Codes.
ZIP+4 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.
For example:
Commercial customers generally apply a ZIP+4 or a delivery point code (i.e., ZIP+6) to mail as part of address normalization. They may need to do so to receive discounted postage rates. The public does not need to write the ZIP+4 code, as mail is read by a multiline optical character reader (MLOCR) that determines the correct ZIP+4 Code from the address—along with the even more specific delivery point—and prints 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, Kivalina, 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).
Postal barcode
The ZIP Code is often translated into an Intelligent Mail barcode 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 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. It must be accompanied by documentation confirming this. These steps are usually done with PAVE-certified software that prints the barcoded address labels and the barcoded sack or tray tags.
The assignment of delivery point digits (the 10th and 11th digits) ensures that every mailable point in the country has an 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.
Relationship with local government boundaries Each ZIP Code has one or more "postal city" names assigned to it. Since a ZIP Code is a collection of delivery points served by a specific physical post office, ZIP Codes often do not coincide with the boundaries of local government units. For example, suburban and unincorporated areas may share a postal city name with a neighboring municipality, even if no part of its ZIP Code is actually within that city.
Structure and allocation
USPS Postal Cities The USPS postal delivery zone is the place name assigned by the USPS to the last two digits of a 5-digit ZIP Code, coded to a corresponding post office physical location. While ZIP Codes designate delivery points within the United States (and its territories) the associated USPS postal city names may not be the names residents of states serviced by the Post Offices identify as where they legally reside. The resulting structure of the ZIP Code does not necessarily follow administrative or political boundaries and may cross state lines. When the 5-digit ZIP Code is followed by +4 digits the four digits can in practice, determine a specific USPS Post Office box number and alternatively, a sector, segment, several blocks or side of the street parcel is delivered from a USPS route. Parcel addressed to a ZIP Code without the corresponding USPS postal delivery zone name is often stamped with a request to update the address or marked return to sender.
The local or state government entity assigning street numbers linked to emergency services, not the USPS, determines legal, physical, addressing. When legal and mailing addresses are not disambiguated on registration forms by separate fields, a USPS postal city often replaces a municipal name. Registration form field restrictions like 'PO BOX not allowed' exist as an internal control on forms without source to standards or regulation. Corporate registration form designers operating in identity collection commerce such as government, immigration, healthcare, real estate, mortgage, utilities and registered agency, tend to utilize zip codes but do not always recognize distinctions in address types.
In certain circumstances where digital forms requesting a legal or physical address use autocomplete formatting for ZIP Code fields; customer applications with valid, deed registered legal physical addresses located within surveyed, incorporated state-chartered municipalities and counties are rejected by corporate registration databases as 'unable to be verified' because the street name and number is associated with the USPS postal city name, not the municipal or county name. As a geographic metric in public health research, USPS postal cities are an arbitrary and unsurveyed geographic designation and remain flawed when applied outside their intended use as became evident in the Flint, MI water crisis.
As a result of the disconnect in application between legal, delivery or mailing addressing many US states opt in to modernized point based, geocoded, address data standards like NENA, ANSI and collection platforms like the USDOT National Address Database (NAD) to provide reference to legal addresses for essential and emergency services as an alternative to a traditional USPS ZIP Code Boundary Review Process.
Types There are four types of ZIP Codes:
Unique: assigned to a single high-volume address Post office box-only: used only for PO boxes at a given facility, not for any other type of delivery Military: used to route mail for the U.S. military Standard: all other ZIP Codes.