Codes used within postal addresses to indicate a geographic area, point or route or as a pointer to a company or building. Used to improve postal sorting and delivery and to prevent confusion when two streets share the same name within a single populated place.
Note: Postal code is the generic term for a code used in a postal address to aid in sorting and delivery. Other terms are used by particular postal authorities. There is a variation in terminology between language (Postal Code, Code Postal, Código Postal, Kody pocztowe) and also within languages (Postal Code, Postcode, ZIP Code, PIN Code etc.)
Considerations
Coverage. Postal codes can point to a range of geographic areas, users or mailing addresses. A postal code may cover:
A whole country
A single postal code covers all addresses in Anguilla.
A Region.
A single settlement or municipality
Postal codes in Belgium cover municipalities
A district of a populated place
A range of streets
A single street
A range of buildings
Dutch postal codes each cover a small number of buildings, post office boxes or users.
A single building
A single company or other large-user
A mailing address range (post office boxes, routes etc.)
In some countries each postal code covers a similar number and size of delivery points. In others, coverage varies.
The size of an area covered by a single geographic postal code can vary immensely.
Australian postal code boundaries, showing the huge size differential between postal code districts.
Even in countries where postal code systems ostensibly match administrative district boundaries, there are often exceptions caused by inertia in one system as the other changes or for pragmatic purposes such as allowing better mail delivery to those areas concerned.
Example: In the United States of America the ZIP Code can usually be used to define state, but there are exceptions. For example:
Fishers Island, New York, bears the ZIP Code 06390 and is served from Connecticut because the only ferry service is to Connecticut – all other New York ZIP codes (excepting those at Holtsville for the Internal Revenue Service (IRS)) begin with "1".
Some Texas ZIP Codes are served from New Mexico (most notably some El Paso ZIP codes) and thus bear codes beginning with "885" (contiguous numerically with 870-884 NM) rather than "799".
Some Arkansas roads north of Bull Shoals Lake can best be accessed by the Protem, Missouri, delivery unit (ZIP Code 65733).
Addresses in Cox Sisters Road in Virginia are best accessible from North Carolina and they use the North Carolina ZIP code for Sparta - 28675
Cincinnati/Northern Kentucky International Airport, despite being located across the Ohio River from Cincinnati in Hebron, Kentucky, uses ZIP Code 45275 for mailing only, due to the fact the Kenton County Airport Board, which owns and operates the airport, maintains a PO Box physically located at the main post office in Cincinnati. The physical address of the airport is 2939 Terminal Drive, Hebron, Kentucky, 41048. In essence the mail for the Kenton County Airport Board has an Ohio ZIP code but the physical address of the airport is a Kentucky ZIP code.
Postal codes have a number of lengths or formats throughout the world. They may be numeric or alphanumeric, and may contain punctuation. At the current time they may contain upper case letters (A-Z, without diacritical marks), numbers and/or punctuation)
Many countries and territories do not have a postal code system.
Countries and territories without a postal code system, correct as of March 2020 (including countries with postal codes in development or with only partial coverage): Angola, Antigua & Barbuda, Aruba, Bahamas, Belize, Benin, Bolivia, Bonaire, Botswana, Bouvet Island, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Comoros, Congo (Brazaville ), Congo (Kinshasa), Cook Islands, Curaçao, Djibouti, Dominica, East Timor, Equatorial Guinea, Eritrea, Fiji, Gabon, Gambia, Ghana, Grenada, Guyana, Hong Kong, Ivory Coast, Jamaica, Kiribati, Libya, Macao, Mali, Mauritania, North Korea, Qatar, Rwanda, Saba, Sao Tome & Principe, Seychelles, Sierra Leone, Sint Eustatius, Sint Maarten, Solomon Islands, Suriname, Syria, Togo, Tokelau, Tonga, Tuvalu, Uganda, United Arab Emirates, Vanuatu, Yemen, Zimbabwe.
Large users in some countries may have three different postal codes - one geographic, one for a post office box, and one large-user code.
An address block may correctly contain more than one postal code
Example: Serbia currently uses both a 5-digit postal code and a 6-digit postal code in the same address:
Given the time lag required to update and release postal code data files, and the rule that no data file is 100% correct, new addresses may not appear in existing postal data files, and those data files may contains addresses which no longer exist.
There is a difference between a postal code and a sorting code. A sorting codeoften appears after a place name to provide information additional to any postal code. For example, in 1000 Brussel X, the 1000 is the postal code and the X a sorting code to indicate a specific post office within that area. In general, postal code systems geographically cover a whole country whereas sorting codes are used for specific areas or addresses only, such as with Dublin in the Republic of Ireland.
A single building may have more than one postal code, especially when it is occupied by multiple large users.
Postal codes may commence with one (or more) zeroes.
Countries and territories with postal codes which may commence with a zero (not an exhaustive list): Algeria, Armenia, Australia, Cambodia, Finland, France, Germany, Guatemala, Holy See, Italy, Laos, Maldives, Nepal, Puerto Rico, Romania, Slovakia, Spain, Ukraine, United States of America, United States Virgin Islands.
For example:
340 Tiburtina Valeria 00011 ROMA ITALY
Postal codes appear in different places within an address block according to the country. Examples:
Postal codes can also fall foul of obscenity screening. Examples: V4G 1N4, Delta, British Columbia, Canada. Map
A place may have a postal code from more than one country.
Example: Because physical access to the settlements of Büsingen in Germany and Campione d’Italia in Italy is easier through Switzerland, they have been ascribed the following postal codes by the Swiss Post Office:
8238 BÜSINGEN (German postal code 78266) 6911 CAMPIONE D'ITALIA (Italian postal code 22060)
Example: Northern uses Cypriot 4-digit postal codes, but for mail from, or routed via, Turkey, a Turkish 6-digit code commencing 922 is used.
A country or territory may not have its own postal code system, but may be given codes by another country.
Example: Hong Kong and Macao do not have postal code systems, but for post from China the postal code 999077 has been assigned to Hong Kong and 999078 to Macao.
A country or territory may be covered by the postal code system of another country.
Example: Liechtenstein is part of the Swiss postal area; San Marino and Holy See are part of the Italian postal area; Marshall Islands, Micronesia and Palau are part of the United States of America postal area.
Processing
Do not make "postal code" a required field for countries and territories which do not use postal codes or for those where postal codes are not widely disseminated or adopted. Not all customers will know their postal code, or even that a system exists in their country.
On customer-facing forms you can use a localised name for postal code if you know the country in which the postal addresses is situated. Otherwise, use the generic term postal code. Do not use local forms, such as ZIP, for customers with addresses in other countries.
Resource: Time to Zap the ZIP. Graham Rhind looks at how local versions of "Postal code" on input forms confuse users. (Cached version)
Postal codes are formed in different ways in different countries. Do not limit any field, input form or processing to suit only the postal code format of a single country.
Validation:
Allow postal code fields to contain alphabetic characters, digits and punctuation.
Force the field contents to upper-case as there are currently no examples of postal codes written with lower-case letters.
Only allow the alphabetic characters between A and Z - no others (e.g. those with diacritical marks) are currently used in postal codes.
Field lengths : the longest postal code currently in use in the world is 10 digits long.
Map of postal code lengths throughout the world (including spacing and punctuation). Download an updated version, and others with more detailed information, via this page.
Do not attempt to store postal codes in a numeric field, even for countries which have numeric postal codes. In many countries postal code may start with a zero and this is stripped off in numeric fields, damaging the data.
A company or (more rarely) an individual can have up to three addresses: a street address, a mailing address and a large-user address. Depending on the country, each of these may have their own postal code. If stored in a single record, it is therefore necessary to allow three fields to be reserved to store these postal codes.
Store postal codes in a separate field from other address information. It is used in much data processing.
Postal codes may be written preceded by a country code in this way: "B-1000". As this information duplicates the country code which should be stored elsewhere in a database, and can be added on export if required, it can be stripped before storage and processing.
Postal codes appear in different places within an address block according to the country. Ensure that you output it in the correct place to reduce customer irritation and promote optimal delivery efficiency, as in many countries postal information is read and recognised my computers.
A single postal code covers all addresses in Anguilla.
Postal codes in Belgium cover municipalities
Dutch postal codes each cover a small number of buildings, post office boxes or users.
