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In the United States, ZIP codes are a type of postal code. Individuals who mail letters or packages via the United States Postal Services (USPS) are required to write the code as part of the address. This five-digit code helps ensure that parcels get to their intended destination faster. In fact, the acronym zip, which stands for Zone Improvement Plan, suggests speed and swiftness.
By looking at the numbers in these codes, a mail sorter can determine where the parcel should go. Each digit in a ZIP code stands for specific areas or regions of the United States (US). Some stand for broad regions, such as the east or west coast, while others stand for specific states, cities, and towns.
The first digit of each code corresponds to a broad regional area. Typically, this is a group of neighboring states. For example, codes beginning with zero represent the New England states, including Maine, Massachusetts, Vermont, and Connecticut. They also represent US territories, like Puerto Rico and the US Virgin Islands.
Zip codes that begin with the number nine, on the other hand, typically represent states along the west coast. California, Oregon, and Washington all have codes that begin with nine, for instance. Alaska and Hawaii also have zip codes that begin with nine.
The next two digits represent a specific sectional center facility. These USPS facilities are responsible for sorting the mail even further. Many times, they are located in large metropolitan areas.
The last two digits represent an even more specific area, usually a post office. This is located within the region represented by the first digit. It is also typically close to the sectional center facility.
Some addresses that manage a large volume of incoming mail may have their own zip codes, known as unique zip codes. For example, the White House has the zip code 20006. Other government buildings in the US also have been assigned codes that start with 202 through 205, regardless of where they are located. Universities and other similar facilities may also have unique postal codes.
Although it is not required, sometimes a parcel is addressed using nine-digit codes. This type of code is sometimes referred to as a ZIP+4 code. These codes are written with the first five digits, followed by a hyphen, followed by the additional four digits. These last four numbers narrow a location down even more, and many times they represent a specific block or street.
I know how bad my own handwriting can be, so I'm surprised that more mail isn't misdirected because of an illegible number or two. The mail handlers and sorting computers must be used to interpreting squiggly lines pretending to be numbers.
I can see where a zip code would be an efficient way of sorting the incredible volume of mail that arrives at a postal facility. One employee wouldn't have to know what each and every number represented. The first mail handler would just look at the first number and send it to the corresponding bin. The process would be repeated at the next facility, where another handler would only care about the next two numbers, and so on. It's better than relying on one handler to read all five numbers at once.