def _geo_field(self, field_name=None):
        if field_name is None:
            # Incrementing until the first geographic field is found.
            for fld in self.model._meta.fields:
                if isinstance(fld, GeometryField): return fld
            return False
        else:
            # Otherwise, check by the given field name -- which may be
            # a lookup to a _related_ geographic field.
            return self._check_geo_field(self.model, field_name)

### Field Classes for `convert_values` ####
Returns the first Geometry field encountered; or specified via the
dataset/ETHPy150Open dcramer/django-compositepks/django/contrib/gis/db/models/sql/query.py/GeoQuery._geo_field