code: function(location) {
          var id = null;
          var info = this.getTileData(location);
          if (info.tile) {
              id = info.tile.getFeatureId(info.i, info.j);
          }
          return id;
      }
docs: APIMethod: getFeatureId
  Get the identifier for the feature associated with a map location.
  
  Parameters:
  location - {<OpenLayers.LonLat>} map location
  
  Returns:
  {String} The feature identifier corresponding to the given map location.
  Returns null if the location doesn't hit a feature.