NPA (Numbering Plan Area)

NPA (Numbering Plan Area) is encoded numerically with a three-digit telephone number prefix, commonly called the area code. Each telephone is assigned a seven-digit telephone number unique only within its respective plan area. The telephone number consists of a three-digit central office code and a four-digit station number. The combination of an area code and the telephone number serves as a destination routing address in the public switched telephone network (PSTN).

NENA 03-008, NENA Standard for E9-1-1 Default Assignment and Call Routing Functions