def get_area_def(self, dsid):
        """Get area definition for message.

        If latlong grid then convert to valid eqc grid.

        """
        msg = self._get_message(self._msg_datasets[dsid])
        try:
            return self._area_def_from_msg(msg)
        except (RuntimeError, KeyError):
            raise RuntimeError("Unknown GRIB projection information")