American ZIPs
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 (or perhaps a large city) and the fourth and fifth digits representing a group of delivery addresses within that region. The main town in a region (if applicable) 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 an adjacent state (q.v.).
Generally, the first three digits designate a sectional center facility, the mail-sorting and -distribution center for an area. 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 an appropriate location for a center in that region. For example, 739 in Oklahoma is assigned to Liberal, Kansas; 865 in Arizona is assigned to Gallup, New Mexico; and 961 in California to Reno, Nevada.
Geographically, many of the lowest ZIP codes are in the New England region, since these begin with ‘0′. Also in the ‘0′ region are Puerto Rico, the U.S. Virgin Islands and APO/FPO military addresses for personnel stationed in Europe. The lowest ZIP code is in Holtsville, New York (00501, a ZIP Code exclusively for the U.S. Internal Revenue Service center there). Other low ZIP codes are 00601 for Adjuntas, Puerto Rico; 01001 for Agawam, Massachusetts, and 01002 for Amherst, Massachusetts. Up until 2001 there were also six zip codes even lower than 00501 that were numbered from 00210 to 00215 (located in Portsmouth, New Hampshire) and were used by the Diversity Immigrant Visa program to receive applications from non-US citizens.
The numbers increase southward along the East Coast, such as 02115 (Boston), 10001 (New York City), 19103 (Philadelphia), 20008 (Washington, D.C.), 30303 (Atlanta) and 33130 (Miami) (these are only examples as each of these cities contain several zip codes in the same range). 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, Iowa, 60601 in Chicago, 77063 in Houston, 80202 in Denver, 94111 in San Francisco, 98101 in Seattle, and 99950 in Ketchikan, Alaska.
he first digit of the ZIP code is allocated as follows:
* 0 = Connecticut (CT), Massachusetts (MA), Maine (ME), New Hampshire (NH), New Jersey (NJ), Puerto Rico (PR), Rhode Island (RI), Vermont (VT), Virgin Islands (VI), Army Post Office Europe (AE), Fleet Post Office Europe (AE)
* 1 = Delaware (DE), New York (NY), Pennsylvania (PA)
* 2 = District of Columbia (DC), Maryland (MD), North Carolina (NC), South Carolina (SC), Virginia (VA), West Virginia (WV)
* 3 = Alabama (AL), Florida (FL), Georgia (GA), Mississippi (MS), Tennessee (TN), Army Post Office Americas (AA), Fleet Post Office Americas (AA)
* 4 = Indiana (IN), Kentucky (KY), Michigan (MI), Ohio (OH)
* 5 = Iowa (IA), Minnesota (MN), Montana (MT), North Dakota (ND), South Dakota (SD), Wisconsin (WI)
* 6 = Illinois (IL), Kansas (KS), Missouri (MO), Nebraska (NE)
* 7 = Arkansas (AR), Louisiana (LA), Oklahoma (OK), Texas (TX)
* 8 = Arizona (AZ), Colorado (CO), Idaho (ID), New Mexico (NM), Nevada (NV), Utah (UT), Wyoming (WY)
* 9 = Alaska (AK), American Samoa (AS), California (CA), Guam (GU), Hawaii (HI), Marshall Islands (MH), Federated States of Micronesia (FM), Northern Mariana Islands (MP), Oregon (OR), Palau (PW), Washington (WA), Army Post Office Pacific (AP), Fleet Post Office Pacific (AP)
The next two digits represent the sectional center facility (e.g. 432xx = Columbus OH), and the fourth and fifth digits represents the area of the city (if in a metropolitan area), or a village/town (outside metro areas): 43209 (4=Ohio,32=Columbus,09=Bexley). When a sectional center facility’s area crosses state lines, that facility is assigned separate three-digit prefixes for the states that it serves; thus, it is possible to identify the state associated with any ZIP Code just by looking at the first three digits.[citation needed]
Despite the geographic derivation of most ZIP codes, the codes themselves do not represent geographic regions; they generally correspond to address groups or delivery routes. Consequently, ZIP Code “areas” can overlap, be subsets of each other, or be artificial constructs with no geographic area. Similarly, 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, U.S. government agencies in and around the nation’s capital are assigned ZIP codes starting with 20200 to 20599, which are Washington, D.C., ZIP codes, even if they are not located in Washington itself. While the White House itself is located in ZIP code 20006, it has the ZIP code 20500. The Nuclear Regulatory Commission is located in Rockville, Maryland, at ZIP code 20852, but has been assigned by the Postal Service the address “Washington, DC 20555″. The United States Patent and Trademark Office used to be located in Crystal City, Virginia at ZIP Code 22202 but was assigned by the Postal Service the address “Washington, DC 20231″; however, since its move to Alexandria, Virginia, it uses the ZIP + 4 code 22313-1450.
Similarly, the ZIP code for the Metropolitan Washington Airports Authority, a federally-chartered independent authority, is 20001-6000, even though the physical address of the Authority’s office, “1 Aviation Circle”, is in Arlington, Virginia.[4]
Rarely, a locality is assigned a ZIP code that does not match the rest of the state; in other words, a zip code may cross state lines. Generally, the locality is so isolated that it most conveniently served from a sectional center in another state. Examples:
* Fishers Island, New York, bears the ZIP code 06390 and is served from Connecticut — all other New York ZIP codes (excepting those at Holtsville for the IRS) begin with “1″.
* Some Texas ZIP codes are served from New Mexico and thus bear codes beginning with “8″ rather than “7″.
* Returned government parcels from the District of Columbia are sent to ZIP codes beginning with “569″, so that returned parcels are security checked at a remote facility (this was put into place after the anthrax scare).
* Some Arkansas roads north of Bull Shoals Lake can best be accessed by the Protem, Missouri delivery unit (ZIP Code 65733).
* Fort Campbell (ZIP Code 42223), primarily in Kentucky, also has some roads in Tennessee.