ZIP Codes

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Due to the huge amount of mail, and the revolution in transportation, and the steep rise in manpower costs, there needed to be a change in how mail was delivered in a timely manner. All these things helped produce the ZIP  Code.  ZIP stands for Zoning Improvement Plan.

The Post Office Department moved most of its mail by railroad in 1930. More than 10,000 mail-carrying trains crisscrossed the country, moving round the clock into virtually every village and metropolitan area.

The railroads' peak year may have been 1930. By 1963, fewer trains, making fewer stops, carried the mail. In these same years, 1930-1963, the United States underwent many changes.  The transportation of mail also changed.

Over the years, a number of potential coding programs had been examined and discarded. Finally, ZIP Code would begin on July 1, 1963.

Preparing for the new system was a major task. Mail transportation centers were set up around the nation.  They were called the Metro System. There were 85 of these transportation centers to start with.  Most were located around large cities.  Later the Metro concept had 552 sectional centers and each of these had 40 to 150 post offices.  That makes a total of 22,080 to 82,800 post offices in the United States.

The next step in establishing the ZIP Code was to assign codes to the centers and the postal addresses they served. 

By July 1963, a five-digit code had been assigned to every address throughout the country.  Each digit represents a certain thing.

The first digit represents the broad geographical area of the United States .  You use zero for the first number in the Northeast and nine for the first number in the far West.

This was followed by two digits that represented the Metro centers.

The final two digits represented the small post offices in larger zoned cities.

ZIP Code began on July 1, 1963, as scheduled. Use of the new code was not mandatory at first for anyone, but, in 1967, the Post Office required mailers of second- and third-class bulk mail to presort by ZIP Code. Although the public and mailers alike adapted well to its use, it was not enough.