Zipdy is a program for calculating the distance between two zip codes and finding all the records in a RDBMS with a zip code with x miles of another zip code. Currently, RDBMS support exists for postgreSQL. Additional future support for other databases will be added in future releases of zipdy.
Zipdy is public domain software. Zipdy was written in C but is also available in PHP and perl. It runs with data from the US Census Gazetteer program. The original Gazetteer data is available here. The data is from the 2000 census.
The distance calculations are made by doing a great circle calculation on longitude and latitude points provided by the census data. The result is returned in standard miles. If you need an explanation of what a great circle distance calculation is, click here.
Main Features of Zipdy:
Note: Datafiles where not updated for version 2.5.0. To upgrade, you only need to download the source archive.
If you'd like to place zipdy on your web site just to calculate the distance between two zip codes, you'll need to acquire GDBM support for your platform if you don't have it. Then you'll need to download these files:
Here is the zipdy FAQ. Please read the FAQ before contacting me with questions and requests for support.