US ZIP codes are a form of postal codes used for areas across the United States to help assist the postal service in tracking down the location of certain addresses and route mail more efficiently. Some people still refer to these ZIP codes as postal codes, but the term ZIP stands for zone improvement plan. First of all, the five-digit format for the US postal ZIP code lists was designed in 1963, and this was later extended to provide a further four digits following a dash. The extra numbers provided in US postal ZIP code lists are to help postal service workers code mail more precisely for delivery.

Although the ZIP codes were originally created for the USPS, many other companies offering delivery services, such as FedEx and UPS, now use ZIP codes to help them sort packages, as well as calculate the cost and time associated with shipping a package.

Assigning ZIP Codes:

US postal ZIP code lists can be used to represent a small group of U.S. states. Because they are designed to allow for more efficient mail delivery, some ZIP codes will span a number of different states to help make mail routing and delivery more effective. The first three digits in any code will refer to the central processing facility for mail, where that mail is sorted and processed. The last two digits refer to where the mail is distributed to local post offices.

While a ZIP code plus the additional available four digits is not necessarily required, it assists the post office in sorting additional mail. A ZIP code plus the four extra digits may send mail directly to a group of apartments, city block, or a business that receives a large amount of mail.

US ZIP Code Boundaries:

Although ZIP codes generally seem to be geographic in the way that they are organized, they were not initially intended to be this way. Instead, the purpose of a ZIP code was to allow the USPS to access a method of delivering mail more efficiently. In many cases, addresses located close to one another will be grouped into the same ZIP code, which gives the impression that these codes are defined by geographic boundaries. However, the truth is that some ZIP codes have no connection whatsoever with the geographic location of certain addresses. For example, all US Navy Mail is sent to the same ZIP code.

At this point in time, there is no official map for ZIP codes that outlines the location of different codes according to the USPS data. The reason for this is that there isn't always a geographical boundary available to help sort a ZIP code.

Finding Addresses With ZIP Codes:

If you have a person's ZIP code, you might be able to track down his or her location. However, that will only work if you have the exact and full ZIP code. Alternatively, entering a person's address into an online system may allow you to track down his or her ZIP code for the purpose of documentation, or sending mail and packages.

Click here to find zip codes by state.