Geocoding is the process of calculating the latitude and longitude of an address. You can use that information to calculate the distance from one location to another location -- for example, to provide a directory of stores within a certain radius of a given address.

In a recent discussion of my open-source HTTPAPI toolkit, I provided two different examples of how to use a geocoder web service from an RPG program.

The sample programs use the Geocoder.us website for geocoding. Their site is free for non-commercial use, and they sell commercial licenses if you want to use it for commercial purposes.

In my HTTPAPI discussions, I demonstrated using the Geocoder as a SOAP web service and as a REST web service. Here are links to my messages and the sample code for each:
REST version: http://www.scottklement.com/archives/ftpapi/200707/msg00037.html
SOAP version: http://www.scottklement.com/archives/ftpapi/200707/msg00055.html

Obviously, you need to download my HTTPAPI toolkit to use these examples. HTTPAPI is completely free (open source) and includes sample programs for UPS package tracking, language translation, and currency exchange rates, among other things. You can download it from the following link:
http://www.scottklement.com/httpapi