Like this:
(BTW, in modern times, Maryland is a northeastern state, not a southern state. What it was 150 year ago during the Civil War and Reconstruction doesn't matter.)
The term "
Mid-Atlantic" exists for a reason. I wouldn't go nearly so far as to characterize MD as "northeastern" (DE, probably, but MD is too far south for that), but yes, it's definitely not southern, either.
Imo the South is all of the former Confederacy, excluding TX (huge swaths of it are much more western than southern) and FL (geographically it's Deep South ofc, but the same historical vs contemporary argument you made is very well applied to FL - today, it's got a ton of Midwestern/Northeastern transplants, a lot of Hispanics in the Southeast, etc.; really only the north of it - Little Dixie - can be characterized as southern).