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Our ZIP Code boundaries are used by hundreds of businesses. Here is a brief sampling:

3Com Corporation
3M Corporation
Advance Auto Parts
American Express
American Greetings
Astra Zeneca
Bankers Life and Casualty
Dow Jones
Dr. Pepper
Eastman Kodak
Hewlett Packard
Johnson & Johnson
Live Nation
Maui Jim Sunglasses
McGraw Hill Companies
Merrill Lynch
Michelin Tire
Nestlé HealthCare
Procter & Gamble
The Scotts Company
University of California
USA Today
US Army
US Navy


ZIP Code History

A Brief History of the Development of the ZIP Code in the United States

ZIP Codes have an interesting history beginning with their inception in the early 1960's to their unintended use today in sales and marketing applications, internet technology, data collection and GIS.

ZIP Codes

ZIP Code HistoryThe ZIP code is the system of postal codes used by the United States Postal Service (USPS). The name ZIP, an acronym for Zone Improvement Plan, is written properly in capital letters and was chosen to suggest that the mail travels more efficiently, and therefore more quickly, when senders use it. The basic format consists of five numerical digits. An extended ZIP + 4 code includes the five digits of the ZIP code, a hyphen and then four more digits, which allow a piece of mail to be directed to a more precise location than by the ZIP code alone. ZIP Code was originally registered as a trademark by the U.S. Postal Service but its registration has since expired.


The postal service implemented postal zones for large cities in 1943. For example:

John Hancock

28 Prince St.

Boston 24, Massachusetts

The "24" in the example above is the number of the postal zone within the city.

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. Robert Moon, an employee of the post office, is considered the father of the ZIP code. He submitted his proposal in 1944
while working as a postal inspector.

The post office only gives credit to Moon for the first three digits of the ZIP code, which describe the region of the country. In most cases, the last two digits coincide with the older postal zone number, thus:

John Hancock

28 Prince St.

Boston 24, Massachusetts 02113

Enter Mr. ZIP

Mr. ZIPIn 1967, these were made mandatory for second- and third-class bulk mailers, and the system was soon adopted generally. The United States Post Office used a cartoon character, Mr. ZIP, to promote use of the ZIP code. He was often depicted with a legend such as "USE ZIP CODES" in the selvage of panes of stamps or on labels contained in, or the covers of, booklet panes of stamps. Curiously enough, the only time the Postal Service issued a stamp promoting the ZIP code, in 1974, Mr. ZIP was not depicted. Mr. ZIP promoted the use of ZIP codes for the USPS during the 1960s and 1970s.


Watch an early advertisement of "The Swingin' Six" hoping to persuade people to use ZIP Codes.


ZIP + 4

In 1983, the U.S. Postal Service began using an expanded ZIP code system called "ZIP
+ 4", often called "plus-four codes" or "add-on codes."

A ZIP + 4 code uses the basic five-digit code plus an additional four 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 or any other unit that could use an extra identifier to aid in efficient mail sorting and delivery. Use of the plus-four code is not required except for certain presorted mailings.
In general, mail is read by a multiline optical character reader (MLOCR) that instantly determines the correct ZIP + 4 code from the address and — along with the even more specific delivery point — sprays a Postnet barcode on the face of the mail piece that corresponds to 11 digits. This technology has greatly increased the speed and accuracy of mail delivery and, in turn, kept costs nearly constant for over a decade.

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 58001, Washington DC 20037-8001), zero plus the last three digits of the box number (e.g., PO Box 12344, Chicago IL 60612-0344), or, if the box number consists of fewer than four digits, enough zeros added to the front of the box number to make it a four-digit number (e.g., PO Box 52, Garrett Park MD 20896-0052). However, there is no uniform rule, so the ZIP + 4 code must be looked up individually for each box.

It is common to use add-on code 9998 for mail addressed to the postmaster (to which requests for pictorial cancellations are usually addressed), 9999 for general delivery and other high-numbered add-on codes for business reply mail. For a unique ZIP code
(explained below), the add-on code is typically 0001. Structure and allocation

By geography

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 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; afterward, the numerical order often follows the alphabetical order .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 unique ZIP Code 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 citizens of the six other continents.

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. For example, 40202 is in Louisville, 50309 in Des Moines, Iowa, 60601 in Chicago, 75201 in Dallas, 80202 in Denver, 94111 in San Francisco, 98101 in Seattle, and 99950 in Ketchikan, Alaska. It is important to note that despite the geographic derivation of most ZIP codes, the codes themselves are not geographic regions, but simply categories for grouping mailing addresses. 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.

Rarely, a locality is assigned a ZIP code that does not match the rest of the state. This is when the locality is so isolated that it is served from a sectional center in another state. For example, 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". Similarly, 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).

ZIP codes only loosely tied to cities

An address's ZIP code and the "city" name written on the same line do not necessarily mean that address is within that city. The Postal Service designates a single "default" place name for each ZIP code. This may be an actual incorporated town or city, a sub-entity of a town or city or an unincorporated census-designated place. Additional place names, also of any of these types, may be recognized as "acceptable" for a certain ZIP code. Still others are deemed "not acceptable", and if used may result in a delay in mail delivery.

Default place names are typically the actual city or town that the address is located in. However, for many cities that have incorporated since ZIP codes were introduced the actual city name is only "acceptable" and not the "default" place name. Many databases automatically assign the "default" place name for a ZIP code, without regard to any "acceptable" place names. For example, Centennial, Colorado is divided among seven ZIP codes assigned to "Aurora", "Englewood" or "Littleton" as its "default" place names. Thus, from the perspective of the U.S. Postal Service, the city of Centennial and its 100,000 residents do not exist - they are part of Aurora, Englewood or Littleton. In the ZIP-code directory, Centennial addresses are listed under those three cities. And since it is "acceptable" to write "Centennial" in conjunction with any of the seven ZIP codes, one can write "Centennial" in an address that is actually in Aurora, Englewood, or Littleton, as long as it is in one of the shared ZIP Codes.

"Acceptable" place names are often added to a ZIP code in cases where the ZIP-code boundaries divide them between two or more cities, as in the case of Centennial. However, in many cases only the "default" name can be used, even when many addresses in the ZIP code are in another city. For example, approximately 85% of the area served by the ZIP code 85254, to which the place name "Scottsdale, Arizona," is assigned, is actually inside the city limits of neighboring Phoenix. This is because the post office that serves this area is in Scottsdale. This has led some residents of the ZIP code to believe that they live in Scottsdale when they actually live in Phoenix. A Scottsdale website listing the positive and negative aspects of the city mentioned the 85254 ZIP code as a positive aspect because "Scottsdale" is being used for businesses located outside the Phoenix city limits.

This phenomenon is repeated across the country. The previously mentioned Englewood is a land-locked, inner-ring suburb that was built out by the 1960s. Its post office served the area that is now the high-growth southern tier of the Denver metropolitan area, and ZIP codes in this area were assigned "Englewood" as their "default" place name. An employment center as large as downtown Denver has grown in this area, and its office parks are the headquarters for many internationally recognized corporations. Even though they are actually located in other cities, they indicate "Englewood" as their location, as this is the "default" postal place name. As a result, there
are really two "Englewoods" — the actual city, small and with a largely working-class residential population, and, a number of miles away, the postal "Englewood," a vast suburban area of upscale subdivisions and office parks that have nothing to do with
the City of Englewood yet share a split identity with it solely because of ZIP codes. People who say that they live or work in "Englewood" and identify closely with it may rarely enter the actual city of that name.

"Acceptable place names" also come into play in areas of the country where many citizens identify more strongly with a particular urban center than the municipality they actually live in. For example, Allegheny County, Pennsylvania has 130 distinct municipalities, but many of the county's residents, and even some residents of adjacent counties, commonly use "Pittsburgh, PA" as their postal address.

Finally, many ZIP codes are for villages, census-designated places, portions of cities, or other entities that are not municipalities. For example, ZIP code 03750 is for Etna, New Hampshire, but Etna is not a city or town; it is actually a village district in the town of Hanover, which itself is assigned the ZIP code 03755. Another example is ZIP code 08043, which corresponds to the census-designated place of Kirkwood, NJ but actually serves the entirety of Voorhees Township, NJ. This is also the case in LaGrange, New York, a portion of which is served by the 12603 ZIP code based in the neighboring Town of Poughkeepsie. The rest of LaGrange is served by the LaGrangeville
Post Office. LaGrangeville is itself, not a town at all, but a section of LaGrange.The postal designations for place names become de facto locations for their addresses, and as a result it is difficult to convince residents and businesses that they actually are located in another city or town different from the "default" place name associated with their ZIP codes. Because of the confusion and lack of identity generated by this situation, some cities, such as Signal Hill, California, have successfully petitioned the Postal Service to change ZIP-code boundaries or create new ZIP codes so that their cities can be the "default" place name for addresses within the ZIP code.

This confusion also can have financial implications for local governments, because mail volume is among the factors used by the U.S. Census Bureau to estimate population changes between decennial census enumerations. Sometimes local officials in a community that is not the "default" place name for a zip code but is an "acceptable" place name will advise residents to always use the name of the community, because if the census estimate of that town's population is low they will get less of various State and Federal funds that are computed based on population.

Division and reallocation of ZIP codes

Like area codes, ZIP codes are sometimes divided and changed, especially when a rural area becomes suburban. Typically, the new codes become effective once announced, and a grace period (e.g., one year) is provided in which the new and old codes are used concurrently so that postal patrons in the affected area can notify correspondents, order new stationery, etc.

Most significantly, in rapidly developing suburbs it is sometimes necessary to open a new sectional center facility, which must then be allocated its own three-digit ZIP-code prefix or prefixes. Such allocation can be done in various ways. For example, when a new sectional center facility was opened at Dulles Airport in Virginia, the prefix 201 was allocated to that facility; therefore, for all post offices to be served by that sectional center facility the ZIP code changed from an old code beginning with 220 or 221 to a new code or codes beginning with 201. However, when a new sectional center facility was opened to serve Montgomery County, Maryland, no new prefix was assigned. Instead, ZIP codes in the 207 and 208 ranges, which had previously been assigned alphabetically, were reshuffled so that 207xx ZIP codes in the county were changed to 208xx codes, while 208xx codes outside that county were changed to 207xx codes. Because Silver Spring (whose postal area includes Wheaton) has its own prefix, 209, there was no need to apply the reshuffling to Silver Spring; instead, all mail going to 209xx ZIP codes was simply rerouted to the new sectional center facility.

ZIP codes also change when postal boundaries are realigned. For example, at the same time at which the above-noted change in Montgomery County took place, and under pressure from then-D.C. Mayor Marion Barry, the USPS realigned the postal boundaries between the District of Columbia and Maryland to match the actual boundary. Previously, many inner suburbs, such as Bethesda and Takoma Park, had been in the Washington, D.C., postal area. As a result of the change, ZIP codes in Maryland beginning with 200 were changed to new ZIP codes beginning with 207, 208 or 209, depending on their location, and ZIP codes straddling the D.C.-Maryland line were split. For example, 20014 (Bethesda) became 20814, while the Maryland portion of 20012 (Takoma Park) became 20912.

By type/use

There are three types of ZIP codes: Unique (assigned to a single high-volume address), P.O.-box-only (used only for P.O. boxes at a given facility, not for any other type of delivery) and Standard (all other ZIP codes). As examples of Unique ZIP codes, certain governmental agencies, universities, businesses or buildings that receive extremely high volumes of mail have their own ZIP codes, such as 81009 for the Federal Citizen Information Center of the U.S. General Services Administration (GSA) in Pueblo, Colorado; 30385 for BellSouth in Atlanta; 21412 for Bancroft Hall, the midshipman dormitory at the United States Naval Academy; and 12345 for General Electric in Schenectady, New York. An example of a P.O.-box-only ZIP code is 22313, which is used for P.O. boxes at the main post office in Alexandria, Virginia. In the area surrounding that post office, home and business mail delivery addresses use ZIP code 22314, which is thus a Standard ZIP code.

The above will be made clearer by examining the allocation of ZIP codes in Boston, Massachusetts :

02116 standard deliveries
02117 PO Boxes only (PO Boxes at the main post office)
02212 unique (Bank of America)
02217 PO boxes only (PO boxes at the main post office)
02295 unique (John Hancock Mutual Insurance Company)


While ZIP codes classified as Unique by the USPS always serve a single address, it should not be assumed that a zip code is Unique simply because it serves a single building, complex, or address. Large facilities are often given P.O.-box-only or Standard ZIP codes rather than Unique ZIP codes, because USPS carriers must distribute the mail to multiple boxes, offices, or buildings within the facility. In a Unique ZIP code, mail distribution within the single address is handled internally, rather than by USPS employees.

A few ZIP codes fall outside the three types. APO and FPO ZIP codes are codes in use for U.S. Armed Forces members and their dependents overseas. The state postal abbreviations AP (Area Pacific), AA (Area Americas) and AE (Area Europe) were created in 1991 to serve these communities; previously, APO and FPO mail was addressed to APO San Francisco, APO Miami and APO New York respectively, and APO/FPO ZIP codes were numerically close to the allocations for those cities. The creation of these new state codes necessitated the rewrite of thousands of pieces of postal software and still occasionally causes confusion, as the actual numeric ZIP codes used by the APO/FPO system did not change and are still in use.

Other uses

Delivery services

Delivery services other than the USPS, such as FedEx, United Parcel Service and DHL require a ZIP code for optimal internal routing of a package. This spares customers from being required to use some other routing designator, such as the IATA code of the destination airport or railhead.


ZIP codes are used not only for tracking of mail but in gathering geographical statistics in the United States. The U.S. Census Bureau has data that include the latitude and longitude of the center-point of some ZIP codes (called ZIP Code Tabulation Areas or ZCTAs). The Census Bureau does not keep up-to-date data sets of all ZIP codes. Complete data sets are commercially available.


The data are often used in direct-mail campaigns in a process called ZIP-code marketing, developed by Martin Baier. Point-of-sale cashiers sometimes ask consumers their home ZIP code. Besides providing purchasing-pattern data useful in determining the location of new business establishments, retailers can use directories to correlate this ZIP code with the name on a credit card to obtain a consumer's full address and telephone number. ZIP-coded data are also used in analyzing geographic factors in risk, an
insurance-industry and banking practice pejoratively known as redlining. This can cause problems (e.g. expensive insurance) for people living near a town with a high crime rate and sharing its ZIP code, while they themselves actually live in a relatively crime free town (e.g. south west part of 94303).


ZIP code data is an integral part of dealer/store locator software on many web sites, especially brick-and-click web sites. This software processes a user-input ZIP code and returns a list of store or business locations, usually in order of increasing distance from the input ZIP code.






Source: The information contained on this page is derived from Wikipedia [license] and other sources.