Back in the 1970’s, while living in Chapel Hill, NC, we used to debate the exact location of the “sweet tea line,” above which the default in a restaurant was unsweetened tea and below which it was sweet tea. I recall we finally decided that the line was approximately coincident with I-40/85 as it ran east-west between Winston-Salem and Durham.
Here in Maryland it’s usually unsweetened, but once you cross the Potomac into Virginia they usually give you an option.
By the time you hit the Carolinas, it’s sweet all the way.