Postcodes are used by the US Post Office for more efficient mail delivery. The basic format of the US postal codes consists of five numbers. The first three numbers represent the center of the sections and the other digits represent the older postal code for a particular country or city. The process of using postcodes encoded for US cities came into force in 1943, but in 1963 postcodes were introduced throughout the country.
Part of the central postal code center is the mail handling center. Here, the mail is sorted by the first three digits of the zip code and sent to the proxies in each location. These figures identify the centers across the country. In individual centers, the mail is then sorted by the last three digits and sent to the post offices where recipients receive their mail. Segment centers do not deliver mail and are not open to the public.
By 1967, the second and third mail did not require zip code. After that date, however, it became mandatory for all mail to have the correct postal code in the address. In 1983, the US further expanded the zip code function by creating a Zip Code + 4. These four digits were then used to identify a specific geographic area. In the SCF, the machine identifies the postal code and sends the mail so that it goes to the correct post office.
Today, the first digits of the postal code identify the status or SCF. The second and third digits identify a region of the state and the fourth and fifth numbers identify a specific address in that region. The capital city receives the zip code and then the surrounding cities follow a numerical order.
The distribution of the first postcode number is as follows:
– 0 – Connecticut, Massachusetts, Maine, New Hampshire, New Jersey, Puerto Rico, Rhode Island, Vermont, US Virgin Islands, Army post Europe, Navy post office Europe
– 1 – Delaware, Pennsylvania and New York
– 2 – District of Columbia, Maryland, North Carolina, South Carolina, Virginia and West Virginia
– 3 – Alabama, Florida, Georgia, Mississippi, Tennessee, America's Army Post, America's Navy Fleet
– 4 – Indiana, Kentucky, Michigan and Ohio
– 5 – Iowa, Minnesota, Montana, Montana, North Dakota, South Dakota and Wisconsin
– 6 – Illinois, Kansas, Missouri and Nebraska
– 7 – Arkansas, Oklahoma, Texas and Louisiana
– 8 – Arizona, Colorado, Idaho, New Mexico, Nevada, Utah and Wyoming
Alaska, American Samoa, California, Guam, Hawaii, the Marshall Islands, the Federated States of Micronesia, the Northern Mariana Islands, Oregon, Palau, Washington, the Pacific Ocean Post Office and the Pacific Ocean Navy Post Office.
Postcodes can also be divided and changed when a rural area becomes a suburb of a larger city. The new codes take effect after they are announced, but there is a grace period that allows residents to get used to their new postal code. When a city expands, so that the sectional facility can not cope with the entire mail that comes through it, it is sometimes necessary to open a new facility, which then gets its own number. This also changes the zip code for people living in this area.