The United States Postal Service assigns ZIP codes according to the geographical location and delivery route of the postal address. This allows for mail to be routed to the service centers that handle the mail for those locations.
ZIP codes are a system of postal codes that allow for the efficient distribution of mail throughout the different service centers in the United States. ZIP codes consist of five digits, and may include an optional four digits.
The first digit of a ZIP code represents the state or group of states to which the address belongs. The second and third digits represent a region within the state or states to which the first digit refers. These two digits indicate the Sectional Center Facility to which all mail for that area is routed for processing.
The fourth and fifth digits indicate the particular city, town or village associated with the ZIP code. These last two digits indicate the post office in charge of the delivery of mail to the specified address. A ZIP code may include an additional four digits, known as the "ZIP +4." The purpose of these additional four digits is to identify certain city blocks, buildings or specific recipients with high mail traffic.