In Scotland they are largely based around the 1975 - 1996 districts, whereas in Wales they are based on districts (the second-tier administrative divisions which functioned between 1974 and 1996) or counties. The individual AOSs are between 400 km2 and 4,000 km2 in size.
In Scotland, they are primarily centered around the 1975-1996 districts, while in Wales, they are based on administrative divisions (the second-tier administrative units that operated between 1974 and 1996) or counties. The individual AOSs range from 400 square kilometers to 4,000 square kilometers in size.