• Geographic Division: NPAs divide the service areas for telephone networks. Each NPA is associated with a specific geographic region, which can be a part of a city, an entire city, or multiple cities in a state or province.

• Three-Digit Codes: In the NANP, an NPA is represented by a three-digit code that precedes the local seven-digit telephone number. This makes up the standard ten-digit format used for dialing phone numbers.

• Purpose: The primary purpose of NPAs is to facilitate the organization and allocation of telephone numbers, allowing efficient call routing and management within and between regions.

• Allocation and Management: The allocation of NPAs is managed by regulatory authorities (like the Federal Communications Commission in the U.S.) and administered by the North American Numbering Plan Administration (NANPA).

• Expansion and Overlay Plans: Due to the increasing demand for telephone numbers, new NPAs are occasionally added to regions. Overlay plans, where a new NPA is added to the same geographic region as an existing NPA, are also common to increase numbering capacity.

Numbering Plan Areas are fundamental in structuring telephone networks and services, providing a systematic approach to managing the vast number of phone numbers required for modern communication.