Check to see if the requested tile is part of the tile map.

def is_valid_tile(self, x, y):
        """Check to see if the requested tile is part of the tile map."""
        x = int(x)
        y = int(y)

        if x < 0:
            return False
        if y < 0:
            return False
        if x > self.size_in_tiles.X:
            return False
        if y > self.size_in_tiles.Y:
            return False

        return True