title: Search within a bounded box on a related model using Geocoder Gem
body: <p>In my search action, I am building up a query to list activities.  I would like to be able to limit those to activities whose location is within 5 miles of a centre point and order the activities by distance from centre point. </p>
  
  <p>Its simple enough to get a list of locations:</p>
  
  <pre><code>Location.within_bounding_box(Geocoder::Calculations.bounding_box([location[:latitude], location[:longitude]], 20))  
  </code></pre>
  
  <p>but how can i search the activities model using bounding_box and order by distance?</p>