fill out their location "city/country"
Kinda says your in Europe. In which case you should have a state column for people from the USA. Then to find people close to a new registered user search for city or country and display them as really close people. If you do the state, you can search on that, exclude the city and display as not so close and alphabetize. If you want to list by distance you will need to get Lon/Lat for every location and do Math.
FYI: My IP puts me 250 miles away from where I really am.