docs: def iterGrid(self, minZoom, maxZoom):
          "Yields the tileBounds, zoom, tileCol and tileRow"
          assert minZoom in range(0, len(self.RESOLUTIONS))
          assert maxZoom in range(0, len(self.RESOLUTIONS))
          assert minZoom <= maxZoom
  
          for zoom in xrange(minZoom, maxZoom + 1):
              [minRow, minCol, maxRow, maxCol] = self.getExtentAddress(zoom)
              for row in xrange(minRow, maxRow + 1):
                  for col in xrange(minCol, maxCol + 1):
                      tileBounds = self.tileBounds(zoom, col, row)
                      yield (tileBounds, zoom, col, row)