Wire Center Boundaries are the basic unit of telecommunications geography and are the geographic area served by equipment within a central office. They describe the organization of the local telephone exchange system. Each Wire Center Boundary serves a unique set of telephone numbers within a fixed geographic area. A telephone number consists of three parts: Area Code (3 digits), Prefix (3 digits) and the Line Number (4 digits). Typically, each Prefix is assigned to one specific Wire Center. This means that numbers are assigned to wire centers boundaries in blocks of 10,000. An example of how the data can be used is when a call center routes a call to the service center within an area code. Wire Center Boundaries have defined coverage areas based on phone numbers. The Wire Center boundary file is available for the entire United States or by individual states.