code: def tile(self, bbox, z=0, format=None, clip=True):
          
          # Tile grid uses 3857, but GeoJSON coordinates should be in 4326.
          tile_srid = 3857
          bbox = getattr(bbox, 'geos', bbox)
          clone = filter_geometry(self, intersects=bbox)
          field = clone.geo_field
          srid = field.srid
          sql = field.name
          try:
              tilew = self.tilewidths[z]
          except IndexError:
              tilew = self.tilewidths[-1]
          if bbox.srid != srid:
              bbox = bbox.transform(srid, clone=True)
          # Estimate tile width in degrees instead of meters.
          if bbox.srs.geographic:
              p = geos.Point(tilew, tilew, srid=tile_srid)
              p.transform(srid)
              tilew = p.x
          if clip:
              bufbox = bbox.buffer(tilew)
              sql = geofn.Intersection(sql, bufbox.envelope)
          sql = SimplifyPreserveTopology(sql, tilew)
          if format == 'pbf':
              return clone.pbf(bbox, geo_col=sql)
          sql = geofn.Transform(sql, 4326)
          return clone.annotate(**{format: sql})
docs: Returns a GeoQuerySet intersecting a tile boundary.
  
          Arguments:
          bbox -- tile extent as geometry
          Keyword args:
          z -- tile zoom level used as basis for geometry simplification
          format -- vector tile format as str (pbf, geojson)
          clip -- clip geometries to tile boundary as boolean