Postal codes in Lower Columbia

The postal codes used in Lower Columbia are 7-9 character alphanumeric strings that correspond to a set of postal addresses or a single, large-volume delivery point.

Formatting
Lower Columbian postal codes are divided into two sections, separated by a hyphen: the first part corresponds to a specific postal district, while the second part identifies a local delivery zone.

Postal districts
The first 3-5 characters in a postal code identify the postal district containing the mailing address, and has the general format AA(A)0(0), where A represents any letter and 0 represents any digit; letters and digits in parentheses are not present in all postal codes. Each postal district corresponds to a rural area, an entire medium-sized city, or a smaller area within a large city. The first letter of every postal district indicates the state in which it is located, while the second (and third, if present) letter indicates the city or town where the post office is located. The one or two digits that follow indicate the specific post office that serves the address.

Local delivery zone
The final four characters (which are all digits) denote a local delivery zone, which corresponds to either a specific addres or a range of addresses. A local delivery zone may cover a small town in its entirety, a large part of a mid-sized city, one side of block in a larger city, a large building, a single institution such as a university or hospital, or a business that regularly receives high volumes of mail.

A full postal code may therefore have the following formats:

AA0-0000

AA00-0000

AAA0-0000

AAA00-0000

In practice, however, not many postal codes of the final format have ever been assigned. At the time the postal codee system was implemented, only larger cities were assigned postal codes with two letters in their postal district codes, and only the largest such cities originally had more than nine postal districts; smaller cities and towns predominantly have postal district codes with three letters and one digit. However, cities that have grown significantly since the postal code system was implemented have had their postal distrcits subdivided, resulting in postal codes in those cities having five-character postal district codes.