in southern Wales, in the south of Wales, in the southern part of Wales? [closed]

Can you tell me which one is correct? And if there is a difference in meaning between them, can someone explain it to me?

and here is the example of the sentence

Cardiff is the capital and the largest city of Wales, located
a) in southern Wales
b) in the south of Wales
c) in the southern part of Wales

Solution 1:

Hee, hee. All of them are ‘wrong’ in the sense that they are not standard usage in Britain.

South Wales

…is what people say (and have been saying for a long time, hence New South Wales, the former British colony and now a state in Australia).

See, for example the Wikipedia entry, this tourist guide and a newspaper, The South Wales Argus.