mixed numbers:
The hidden meaning
of everyday digits
U.S. Postal Zip Codes
Using the U.S. Mail was a very different experience in the 1930s than it is today. As described by the U.S. Post Office's own history, railroad was still the primary means of transporting mail, and every item was resorted and redistributed at every stop; 10,000 trains crisscrossed the country delivering mail 24 hours a day.
For the next thirty years, the U.S. underwent many changes; the character, volume, and transportation of its mail followed suit.
By 1962, the railroads were in a state of decline, and business mail had increased to 80% of total mail volume (due in part to the emerging use of computers). A Post Office Advisory Board appointed by the President stated as a top priority the development of a coding system to lessen postal center burden and increase the service speed.
As a result, the Zoning Improvement Plan (ZIP) code system began on July 1, 1963.
The Metro System, from which the ZIP code was developed, was a plan to relieve large mail centers of volume by building up 85 mid-sized cities as mail centers themselves. These new centers, in turn, would be responsible for the distribution of mail to surrounding post offices.
Every address in the U.S. was assigned a 5-digit code when the program began, based on the following system:
- An initial digit representing general geographic region (ranging from 0 in the Northeast to 9 in the Far West).
- A second and third digit designating the address's location within the region's mail centers accessible to common transportation networks.
- Two final digits identifying the specific post office within the region or section.
In 1983, the Post Office expanded the original five-digit zip code to include a four-digit suffix, created the ZIP+4 nine-digit number that is the standard today. These four digits carry additional meaning and aid in the automation of the delivery process:
- The first two digits of the prefix denote a delivery sector within the original five-digit ZIP area-- a few blocks, an apartment complex, a wall of post office boxes, a large office building.
- The final two digits of the prefix refer to a specific delivery segment within that sector-- a floor in a building, houses on one side of the street, a subgroup of post office boxes.
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© Patrick Williams 2003-2004
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