>On Web sites where the user has to enter his postal code or zip code in his profile, this is often used for the proximity search. On a Web site I am hosting, I need to provide that type of search. So, a user could search for people around him within a 50km radius. I believe this is often related to a numeric ID associated to the postal code or to the zip code. Otherwise, the only other thing I would see would be to use the IP address, but then, this is no longer valid is the user is traveling.
>
>So, basically, is there some kind of table that exists for that or how does that work exactly?

Here is an interesting thread on this topic http://tek-tips.com/viewthread.cfm?qid=1529319&page=1 It was discussed by the same person on other sites too, I may find different discussions later about this kind of calculations.