A zip code database is available on the United States Zip Codes organization website as of 2015. The site's geographic map allows a user to view zip codes in his area, search for a specific zip code or search for an address to determine its zip code.
The United States Postal Service created zip codes in 1963, with the word "zip" serving as an acronym for "zone improvement plan." Zip codes were five digits long until 1983, when certain codes had a hyphen and an additional four digits added to make the code more accurate.
The classifications of zip codes are military, post office box only, unique and standard. Military zip codes are used for sending mail to the U.S. military. Post office box only zip codes are associated with a post office and are only used for mail sent to that post office. Unique zip codes are also used for a single location that receives a large amount of mail, such as the Central Intelligence Agency. All other zip codes are in the standard classification.
A zip code's first digit usually corresponds to a group of states. The postal service uses the first three digits to determine which mail facility processes the mail. That facility then sends the mail to local post offices based on the last two digits.