History and Use of ZIP Codes.

In order to help the United States Postal Service route mail more efficiently, ZIP codes were created to be used as a postal code within the United States. “ZIP” is an abbreviation of Zone Improvement Plan. Though ZIP codes were originally developed for United States Postal Service, many other institutions such as Federal Express, United Parcel Service, DHL, and others make use of ZIP codes for sorting packages and calculating the time and cost of shipping a package.

With the original idea for this framework proposed as early as 1944, the structured framework for organizing mail was finally implemented in the early 1960s, with a non-mandatory five-digit code becoming standard nationwide. The first three digits of the ZIP Code would describe the sectional center facility. The mail is then sorted according to the final two digits and sent to the corresponding post offices.

By the mid-80’s, following the success of the zip code system, the United States Postal Service provided an addition to the standard five-digit code. Often called "plus-four codes", the ZIP+4 Code uses the original five-digit code and four additional digits to identify a geographic section within a specific area and assist the United States Postal Service more precisely group mail for delivery. While the ZIP+4 code is not required, it has been determined to help the post offices in the sorting of mail by sections. These sections would often identify industrial segments such as city blocks, apartment groupings, high-volume mail receivers, or any unique unit that requires aid in the mailing and delivery of mail.

There are four types of ZIP Codes. The first is called the unique zip code, which is assigned to a single high-volume address. High volume addresses can include universities and government institutions that receive such extremely high volumes of mail that need their own ZIP Codes. The Post Office Box only ZIP Code is used only for PO Boxes and not meant for any other type of delivery. The third type of ZIP code is military, which is used to route mail for the United States military. All other ZIP Codes are simply called standard ZIP Codes.

The first digit of the ZIP code represents a group of U.S. states which are assigned in order from the north east to the west coast. The next two digits of a ZIP code represent the central mail processing facility, also called sectional center facility which is used to process and sort the mail prior to delivery.

At first-glance, ZIP codes may appear to be based on geography and in most cases, addresses in close proximity are grouped within the same ZIP code. While this may give the appearance that ZIP codes are defined by a clear geographic boundary, it is not the case. The main purpose for ZIP Codes is to group mail and allow the United States Postal Service to deliver mail more efficiently. This means that some ZIP codes can even span multiple states, if deemed more efficient. If it is more efficient for a courier to drive across a state line to deliver mail, the ZIP code will not prevent it.

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