var maxDistance = Number(query.distance);
  var limit = Number(query.limit);
  var page = Math.max(0, query.page);

  var loc = [];
  loc[0] = Number(query.lon);
  loc[1] = Number(query.lat);

  User.find({
      loc: {
        $near: loc,
        $maxDistance: maxDistance
      }
    }).limit(limit).skip(limit * page).sort({username: 'asc'}).exec(function(err, locations) {
            // ....
    });


    // User schema
   /*
     ....
     loc: {
       type: [Number],
       index: '2d'
     }
     ....
   */