code: function(tileData1, tileData2){
              var result = {},
                  key, val;
              for(key in tileData1){
                  result[key] = tileData1[key];
              }
              for(key in tileData2){
                  val = tileData2[key];
                  if(val !== false && val !== void 0){
                      result[key] = val;
                  }
              }
              return result;
          }
docs: Merges 2 `tileData` objects.
  Used to Merges layers of the same tile before drawing them.
  @method mergeTileData
  @param {TileData} tileData1 - `tileData` to merge to.
  @param {TileData} tileData2 - `tileData` to merge from, properties with values on tileData2 replace matching properties on tileData1
  @return {TileData} A new `tileData` object with merged values.