code: def get_all_regions_with_tiles(self):
          
          for key in self.get_all_keys():
              (layer, rx, ry) = struct.unpack('>BHH', key)
              if layer == 1:
                  yield (rx, ry)
docs: Generator which yields a set of (rx, ry) tuples which describe
          all regions for which the world has tile data