title: google app engine : query geohash
body: <p>I have a db.StringProperty() of geohash, by given a hashcode, how do I find the closer 10 result?</p>
  
  <p>I tried below but doesn't seem to be right</p>
  
  <pre><code>pois = POI.all().filter('geohash &lt;', h_latlng).order('-geohash').fetch(10)
  </code></pre>