These definitions and the associated qualifying criteria have been revised as part of the new combined GBTS/GBDVS survey to align with agreed international standards.
Mae’r diffiniadau hyn a’r meini prawf cymhwyso cysylltiedig wedi cael eu diwygio fel rhan o’r arolwg GBTS/GBDVS cyfun newydd i gyd-fynd â safonau rhyngwladol y cytunwyd arnynt.