US ZIP code classification

ZIP codes are classified in the following way:

• Unique - Unique zip codes are used by addresses that get high volumes of mail like universities, agencies, businesses and etc.
• P.O.-box-only - P.O.-box-only zip codes are assigned only to P.O. boxes at a particular facility.
• Military - The U.S.A. military is used military zip code to route mail.
• Standard - Standard zip codes are all other ZIP codes.

US ZIP code: latitude and longitude

ZIP codes of the United States are also used to gather geographical statistics. Latitude and longitude is determined in the center-point of a ZIP code. This center-point is called ZIP Code Tabulation Area.