 One issue with the original work done by Amerine and Winkler was that it did not specify a lower class limit for Region I (originally 2500 or less) or an upper class limit for Region V (originally 4000 or greater).Subsequent research using high resolution spatial climate data identified these limits for California, Oregon, Washington and Idaho, along with Australia.The results provided a lower bound to Region I of 1500 F° units (850 C° units) and an upper bound to Region V of 4900 F° units (2700 C° units).