 Every place in the countries and territories of the NANP belongs to a numbering plan area.Assigning a new area code requires either geographically splitting an existing numbering plan area (split plan) and reassigning the subscribers in the new, smaller area to a new area code, or assigning an additional area code to an existing numbering plan area, which is called an overlay plan.The first new area codes were geographic splits, until the geographical areas were at risk of becoming unreasonably small.