Seeking overlap algorithm

Hi gang: This post is related to the zip lat/long request I recently made and received such an overwhelming response -- many thanks to all. In any event, let's say we have a end-user who is looking for services within his zip-code AND we have a dB of service providers who are willing to render service within a set distance (like 50 miles) from their location. Now, it's a simple matter to convert the user's zip code to lat/longs and then find out how many service providers there are within their area and then show that list to the end-user. That's not the problem. The problem is, could you guarantee to a "preferred" service provider that they would receive top-listing 25 percent of the time? Keep in mind that preferred service providers will overlap. So, the question is how to accommodate for that overlap? If anyone has an algorithm, I would be interested in hearing it. Cheers, tedd -- ------- http://sperling.com http://ancientstones.com http://earthstones.com