How Do Postal Codes Work?

A postal code, also known as a Post, PIN or ZIP code, is a series of letters and/or numbers assigned to an address for the purpose of sorting mail accurately.  In most cases postal codes refer to a geographic location, although, sometimes a postal code may be given to a single address where large volumes of mail are received, such as a government agency or large commercial building.

Although the International Organization for Standardization (ISO) has suggested incorporating a universal system for post codes based on their ISO 2-alpha country code, presently each country with a postal code system administers that system on their own.

In most cases, a countries zip code system can be broken down into some sort of hierarchy, where the first characters may refer to a broad region or administrative boundary.  Each additional character will then increase the geographic resolution until finally there is an exact delivery point for every address.  For example, in the United State, the first character in the 9 to 11 digit post code refers to a region (North East, South West, etc.).  The first three characters can be used to identify the state, and the next two characters identify the city / town with in the state, and so on until the last two digits, which are based on the last two digits of a house or business address, shows the exact delivery point.

As mentioned, the format and make up of a postal code varies from country to country.  In some countries the standard format requires the postal code to be stated at the beginning of an address, while in others, the postal code is the last part of the address.  Furthermore, some country’s postal code are entirely numeric, while others use an alphanumeric version.  Whatever the case, the sole purpose of a postal code is to identify the location for which a mail piece is to be delivered, allowing for easy and accurate sorting of the mail