def __init__(self, extent=(-180.0, -90.0, 180.0, 90.0), tolerance=0.05, **kwargs):
        # Oracle Spatial specific keyword arguments.
        self._extent = extent
        self._tolerance = tolerance
        # Calling the Django field initialization.
        super(OracleSpatialField, self).__init__(**kwargs)
Oracle Spatial backend needs to have the extent -- for projected coordinate
dataset/ETHPy150Open dcramer/django-compositepks/django/contrib/gis/db/backend/oracle/field.py/OracleSpatialField.__init__