Documentation : Summary ( Free Service )
This service is a custom built API that was built by The Easy API. It uses the latest Zip Code listing from the USPS and then combines data from other sources to make a complete zip code set. The main function behind this is to allow with the use of one zip code to obtain all the zip code's and associated data around them based on a miles radius around the central point zip code.
The miles is not driving distance. It's a "As The Crow Flies" mileage.