code: function(level, x, y) {
              var num = 0;
              var size = {};
  
              //Sum up all tiles below the level we want the number of tiles
              for (var z = 0; z < level; z++) {
                  size = this.gridSize[z];
                  num += size.x * size.y;
              }
              //Add the tiles of the level
              size = this.gridSize[level];
              num += size.x * y + x;
              return num;
          }
docs: private