'Returns a Polygon  corresponding to the region represented by a fictional
Google Tile for the given longitude/latitude pair and zoom level. This
tile is used to determine the size of a tile at the given point.'

def tile(self, lonlat, zoom):

    delta = (self._tilesize / 2)
    px = self.lonlat_to_pixel(lonlat, zoom)
    ll = self.pixel_to_lonlat(((px[0] - delta), (px[1] - delta)), zoom)
    ur = self.pixel_to_lonlat(((px[0] + delta), (px[1] + delta)), zoom)
    return Polygon(LinearRing(ll, (ll[0], ur[1]), ur, (ur[0], ll[1]), ll), srid=4326)
