docs: def to_mapquest_str(self):
          """
          Convert Viewbox object to a string that can be used by
          `MapQuest <http://www.mapquestapi.com/geocoding/#options>`_
          as a query parameter.
          """
          vb = self.convert_srs(4326)
          return '%s,%s,%s,%s' % (vb.left, vb.top, vb.right, vb.bottom)