A zip code is the postal code used by the United States Postal Service. ZIP is an acronym for zoning improvement plan. The zip code consists of five numerical digits. An extended zip+4 code includes the five digits of the zip code plus four digits which allow a piece of mail to be delivered to a specific address.
The postal service implemented postal zones for large cities (such as New York 36, New York) in 1943, but by the early 1960s a more general system was needed, and on July 1, 1963, non-mandatory zip codes were announced for the whole country. In 1967, these were made mandatory for second- and third-class bulk mailers and the system was soon adopted generally. The +4 coding was added in 1983.
The White House has its own secret zip code, separate from the regularly-occurring zip code, for the President and his family to receive private mail.
The zip code is often translated into a barcode called POSTNET[?], that is printed on the mailpiece as well, to make it easier for automated machines to sort the mail. Unlike most barcode symbologies, POSTNET uses long and short bars, not thin and thick bars. The barcode can be printed by the person who sends the mail, or the post office will put one on when they receive it. If the post office does it, they either have a human read the address, or have a machine OCR it. (The automated machinery has the unfortunate tendency to paste the coding over the bottom half-inch of postcards, often obliterating the signature.)
People who send bulk mail[?] can get a discount on postage if they have printed the barcode themselves.
Zip codes are used not only for tracking of mail, but in gathering geographical statistics in the United States. The data are often used in direct mail[?] campaigns in a process called zip code marketing[?], developed by Martin Baier[?]. Zip coded data are also used in analyzing geographic factors in risk, an insurance industry and banking practice pejoratively known as redlining.
Robert Moon, an employee of the post office, is considered the father of the zip code, which was adopted in 1963. He first submitted his proposal in 1944 while working as a postal inspector. The post office only gives credit to Moon for the first 3 digits of the zip code, which describe the region of the country.
In general, zip codes have no intrinsic meaning; however, the area around Concord, Massachusetts has the zip code 01776, representing the year of America's Declaration of Independence, as the Battle of Lexington and Concord was one of the opening battles of the American Revolutionary War (though it took place in April 1775).
Zip codes are numbered with the first digit representing a certain group of states, the second and third digits together representing a region in that group (or perhaps a large city), and the fourth and fifth digits representing more specific areas, such as small towns or regions of that city. The main town in a region (if applicable) often gets the first zip codes for that region; afterwards, the numerical order often follows the alphabetical order.
Geographically, the lowest zip codes are in the New England region such as 02107 in Boston, Massachusetts. The numbers increase southward along the East Coast, such as 10036 (New York City), 20500 (Washington, DC), 30303 (Atlanta, Georgia). From there, the numbers begin increasing heading westward and northward. For example, 40202 is in Louisville, Kentucky, 50309 in Des Moines, Iowa, 60601 in Chicago, Illinois, 75201 in Dallas, Texas, 80202 in Denver, Colorado, 94111 in San Francisco, California, 98101 in Seattle, Washington, and 99950 in Ketchikan, Alaska.
The United States Post Office used a cartoon character, Mr. Zip, to promote use of the Zip code.
Recently National Geographic magazine instituted a regular feature focusing, each month, on one ZIP code in the United States.