title: algorithm to find the nearby friends?
body: <p>I have a python program sitting in server side managing user location informations, each friend has a pair of (longtitude, latitude), given a (longtitude, latitude) point, how I can find the nearby(say within 5KM) friends efficiently?</p>
  
  <p>I have 10K users online...</p>
  
  <p>Thanks.
  Bin</p>