Produced: on or before 5th calendar day monthly
Current Release: April 4, 2018
Distribution Frequency: monthly or quarterly (issue date: January, April, July, October)
Distribution Format: Internet download
The NPA NXX to ZIP code database is built using GIS data layers to accurately determine service area by Zip Code and accurately maps United States telephone area codes and exchanges to 5-digit ZIP Codes.
This mapping is based on the geography of the NPA NXX Rate Center and the ZIP Code boundaries which yields a true representation of the coverage areas.
NPA NXX numbering resources are assigned by Rate Centers. Rate Centers are the regulated geographic service areas that telecom carriers provide service to and because their boundaries are relatively stable it is possible to compare them to USPS postal carrier routes to determine what NPA NXX combinations are used in specific Zip Codes.