The North American Numbering Plan (NANP) divides the territories of its members into geographic numbering plan areas (NPAs). Each NPA is identified by one or more numbering plan area codes, consisting of three digits that are prefixed to each local telephone number having seven digits. A numbering plan area may have multiple area codes assigned, a configuration termed an area code overlay. Area codes are also assigned for non-geographic purposes. The syntax rules for area codes do not permit the digits 0 and 1 in the leading position. Area codes with two identical trailing digits are easily recognizable codes (ERC). NPA codes with 9 in the second position are reserved for future format expansion.