Possible Duplicate:
When is the use of “north” more appropriate than “northern” and vice versa?
Are there any differences in meanings of South vs Southern, North vs Northern, and so on, when used in to modify a location? If yes, what is it?
One example I can think of is that South America normally means the area where Brazil, Argentina, etc. are, and Southern America normally means the southern part of the US. Is this only a special case or is this an instance of a more generalized rule?