docs: function findStoresInRange(location, range, callback) {
    db.collection(stores, function(err, collection) {
      if(err) return callback(err);
  
      var query = {loc: {$geoWithin: {$centerSphere:
          [[location.lng, location.lat] , range / 3959]}}} ;
  
      collection.find(query).toArray(function(err, docs) {
        if (err) return callback(err);
        callback(null, docs);
      });
    });
  }