What is a Postal Code?

Whether you work with direct mail, geocoding or address validation, you probably have heard of the term “postal code” before. It’s a system that divides a region into simple geographic groups, which makes it easy for courier companies and postal departments to automatically sort mails.

Postal codes can consist of numbers, letters or a combination of both, with spaces and punctuation marks being optional. The most common symbols used are the digits from zero to nine, along with the alphabets A to Z. A few additional symbols such as hyphens or periods are also commonly used in some regions.

While most regions have a postal code, some cities and countries have even more specific ones to help them organize their mail distribution systems. In the US, for example, a ZIP Code is a unique five digit number that helps streamline postal deliveries across cities and states.

In the 1980s, a four digit extension called ZIP+4 was introduced that gives senders more precision in their address locations. The first two digits of the extended code identify a small segment of the city (e.g. a side of the street, one floor in a large building or a group of Post Office Boxes).

In many countries, there is also a postal zone or district system that identifies areas within cities. London, for example, was originally divided into 10 zones in 1857, and Dublin has had a postal district number system since 1864. Other regions have similar systems, including the French Cedex system.