Rate Center
NANP · also called ratecenter, exchange area
A geographic area used to define local calling boundaries and to which central-office codes are assigned.
A rate center is a geographically specified area used by carriers to determine the boundaries for local versus toll calling and to which telephone numbering resources (NXX codes and thousands-blocks) are assigned. Each rate center has a name and a defined location.
Rate centers — not cities or ZIP codes — are the geographic unit of the numbering system. An area code covers many rate centers, and a rate center may not line up with any single municipality.
A rate center is not a city. Its boundaries are a telephone-network construct for local-calling and number-assignment purposes, and they frequently cross municipal or ZIP-code lines.