title: Convert from kilometers, (km), to decimal degrees
body: <p>Using <code>scipy.KDTree</code> to do some quick nearest neighbour searches. I'm using <code>KDTree.query_ball_point(pnt, r=some_distance)</code> to do the search.</p>
  
  <p>As my points are lat,long the radius value to search (<code>some_distance</code>) has to be in decimal degrees (I believe). If I wanted to make this accessible to a user, I would expect that distance to be given in Kilometres, meters, miles etc.</p>
  
  <p>What is the best way, with python libs, to convert a distance in km to a decimal degrees value? I'm using numpy, scipy and played a bit with PySAL.</p>
  
  <p>Help appreciated,
  Louis</p>