code: function(tile) {
      var x = tile.x;
      var y = tile.y;
      var xUp = x + 1 < xUpperBound;
      var xDown = x >= 0;
      var yUp = y + 1 < yUpperBound;
      var yDown = y >= 0;
  
      var adjacents = [];
      if (xUp) {
        adjacents.push({x: x + 1, y: y});
        if (yUp) {
          adjacents.push({x: x + 1, y: y + 1});
        }
        if (yDown) {
          adjacents.push({x: x + 1, y: y - 1});
        }
      }
      if (xDown) {
        adjacents.push({x: x - 1, y: y});
        if (yUp) {
          adjacents.push({x: x - 1, y: y + 1});
        }
        if (yDown) {
          adjacents.push({x: x - 1, y: y - 1});
        }
      }
      if (yUp) {
        adjacents.push({x: x, y: y + 1});
      }
      if (yDown) {
        adjacents.push({x: x, y: y - 1});
      }
      return adjacents;
    }
docs: Get the locations adjacent to a given tile in the map.