title: Algorithm to find clusters (min x pts. within y distance of cluster center) of geographical points
body: <p>Given a database of geographical locations (long/lat), what would be the best approach to determining/detecting clusters of locations that are within x miles of the cluster center AND total at least y locations?</p>
  
  <p>e.g. out of 1000 McWidgets in NC, there are 30 clusters each containing 20 or more stores within 7 miles of their respective cluster center.</p>
  
  <p>It's been a long time since my applied math course in college... any help for an old mushy brain would be greatly appreciated.</p>