What Do the Numbers in the Zip Code Mean?
By reading zip code numbers, post office employees can route the letters more directly to their destination, and sort them faster. The first digit designates a broad area, which ranges from zero for the Northeast to nine for the far West.
The two following digits are the code of a central post office facility in that region. The last two digits designate small post offices or postal zones.
Here’s how it works: the United States is divided into 10 large areas. Each area has a number between 0 and 9. Suppose the zip code on the letter you mail is 60635. The first number, 6, tells the postal clerk that the letter goes to zip code area number 6, which is the mid west part of the United States. The next two numbers, 0 and 6, narrow it down to Chicago, Illinois. The last two numbers, 3 and 5, pinpoint the local post office.
In 1983, a hyphen and four-digit code was added to some of the ZIP codes. The ZIP+4 code was implemented when it became difficult to sort mail based only on traditional ZIP codes, but it never quite caught on. The development of sorting technologies shortly after its implementation made it mostly redundant.
The sixth and seventh numbers delineate a “delivery sector,” which may be an office building, a small geographical area, a few blocks, or a large apartment building. The last two numbers stand for a delivery segment, which can be as restricted as the floor of an office building or a specific department in a firm.
Though the development of technologies in the past few decades has seriously diminished the amount of snail mail, ZIP codes are still used for many purposes. A myriad of information — such as age, education level, gender, or race — can be gathered about the population living in specific area based on ZIP codes.