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 Otherwise, the only other thing I would see would be to use the IP address, but then, this is no longer valid is the user is traveling.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?