ZIP Code


The ZIP Code system is the system of postal codes used by the United States Postal Service. The term ZIP was chosen to suggest that the mail travels more efficiently and quickly 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 1, 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 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:


Mr. John Smith
3256 Epiphenomenal Avenue
Minneapolis 16, Minnesota


The "16" is the number of the postal zone in a specific city.

Establishment

By the early 1960s, a more organized system was needed. Non-mandatory five-digit ZIP Codes were introduced nationwide on July 1, 1963. 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. 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 Canada Post Corporation, to avoid confusion with New Brunswick.
Robert Moon is considered the father of the ZIP Code; he submitted his proposal in 1944 while working as a postal inspector.
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 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:


John Smith
3256 Epiphenomenal Ave Apt 601
Minneapolis, MN 55416


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:


John Smith
3256 Epiphenomenal Ave Apt 601
Minneapolis, MN 55416-2931


Commercial customers generally apply a ZIP+4 or a delivery point code 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 that determines the correct ZIP+4 Code from the address—along with the even more specific delivery point—and prints an Intelligent Mail barcode 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, zero plus the last three digits of the box number, 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. However, there is no uniform rule, so the ZIP+4 Code must be looked up individually for each box.

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, 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 -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 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.

Structure and allocation

ZIP Codes designate delivery points within the United States.

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.
Unique ZIP Codes are used for governmental agencies, universities, businesses, prisons, or buildings receiving sufficiently high volumes of mail to justify the assignment to them of exclusive ZIP Codes. Government examples include 20505 for the Central Intelligence Agency in Washington, D.C., and 81009 for the Federal Citizen Information Center of the U.S. General Services Administration in Pueblo, Colorado. An example of a university-specific ZIP Code is 21252, which serves Towson University. An example of a unique ZIP Code assigned to a prison is 81290 for the Federal Correctional Complex near Florence, Colorado. An example of a private address with a unique ZIP Code is that assigned to the headquarters of Walmart. They may also be assigned to a single individual, such as Smokey Bear "20252", or a program, such as the Postal Service's Operation Santa Claus program, under which children are invited to write to Santa Claus at "North Pole 88888".
An example of a PO box-only ZIP Code is 22313, used for boxes at the main post office in Alexandria, Virginia, including those used by the United States Patent and Trademark Office. In the area surrounding that post office, home and business mail delivery addresses use ZIP Code 22314, a standard ZIP Code.

Geographic hierarchy

Primary state prefixes

ZIP Codes are numbered with the first digit representing a certain group of U.S. states, the second and third digits together representing a region in that group, and the fourth and fifth digits representing a group of delivery addresses within that region. The main town in a region often gets the first ZIP Codes for that region; afterward, the numerical order often follows the alphabetical order. Because ZIP Codes are intended for efficient postal delivery, there are unusual cases where a ZIP Code crosses state boundaries, such as a military facility spanning multiple states or remote areas of one state most easily serviced from a bordering state. For example, ZIP Code 42223 serves Fort Campbell, which spans Christian County, Kentucky, and Montgomery County, Tennessee, and ZIP Code 97635 includes portions of Lake County, Oregon, and Modoc County, California.
The first three digits generally designate a sectional center facility, the area's mail sorting and distribution center. A sectional center facility may have more than one three-digit code assigned to it. For example, the Northern Virginia sectional center facility in Merrifield is assigned codes 220, 221, 222, and 223. In some cases, a sectional center facility may serve an area in an adjacent state, usually due to the lack of a proper location for a center in that region. For example, 739 in Oklahoma is assigned to Amarillo, Texas; 297 in South Carolina is assigned to Charlotte, North Carolina; 865 in Arizona is assigned to Albuquerque, New Mexico; and 961 in California to Reno, Nevada.
Many of the lowest ZIP Codes, which begin with '0', are in the New England region. In the '0' region are New Jersey, Puerto Rico, the U.S. Virgin Islands, and APO/FPO military addresses for personnel stationed in Europe, Africa, Southwest Asia, and onboard vessels based in the waters adjoining those lands. The lowest ZIP Code is in Holtsville, New York. Other low ZIP Codes are 00601 for Adjuntas, Puerto Rico; 01001 for Agawam, Massachusetts, and the ZIP Codes 01002 and 01003 for Amherst, Massachusetts; 01002 is used for mail in town, while the University of Massachusetts Amherst primarily uses 01003. Until 2001, there were six ZIP Codes lower than 00501 that were numbered from 00210 to 00215 and were used by the Diversity Immigrant Visa program to receive applications from non-U.S. citizens.
The numbers increase southward along the East Coast, such as 02115, 10001, 19103, 21201, 20008, 30303, and 33130 . From there, the numbers increase heading westward and northward east of the Mississippi River, southward west of the Mississippi River, and northward on the West Coast. For example, 40202 is in Louisville, 50309 in Des Moines, 60601 in Chicago, 63101 in St. Louis, 77036 in Houston, 80202 in Denver, 94111 in San Francisco, 98101 in Seattle, and 99950 in Ketchikan, Alaska.
The first digit of the ZIP Code is allocated as follows: