How are phone number area codes located?

Telephone area codes are associated with geographic locations. In the United States and Canada, the North American Numbering Plan assigned these numbers starting in 1947. However, there are currently several services allowing the consumer to set a complete 10-digit telephone number regardless of the area.

At first, each state or province assigned a single area code with a central digit of 0, and assigned multiple had a central digit of 1. For convenience with rotary dialing, the areas with the highest populations also had the lowest digits. This is why, for example, the New York City area has the area code 212. In North America, a single area code corresponds to part of a state or province.