About Zip Codes in USA A Zip code is usually written in the address note. People living in the United States use Zip codes to determine the location of other people. A Zip code is a special code that has been assigned to every city in the United States. Zip stands for 'Zone Improvement Plan' and the purpose of having zip codes is to make things easier for everybody to locate the address where they have to deliver a package, a letter or a courier. Earlier postal codes were used because of the less population, but as the population got increased, administrators divided a city into many zones and each of these zones were handed a zip code. This division has made things easier for the postal service, shippers and recipients due to the standardization formats for zip codes. USPS also benefitted a lot from the zip codes. Zip code is a five digit number in which the first three digits will define the sectional facility and the last two digits will represent the state it belongs to. Google Map services are used to get the most accurate information about the address or location for any particular zip code.