I have a web application to which I need to add automatic scheduling - which entails mapping the shortest route between service calls.

I thought that perhaps the web service that plots the distance between the geographical center of each zip code might be the way to go, even though it may be flawed when dealing with addresses near the boundaries.

I also seem to remember an article in FPA from many moons ago that discussed this kind of thing, but I can't seem to find a reference at their web site.

Any thoughts or suggestions?