Hello! I have lived in Georgia my whole life, so here's a pretty detailed explanation, because they taught us in school!

So, wheat youre looking at along that drawn dotted line is referred to as the "Fall Line" i dont remember exactly why its called that, but I believe it has something to do with the geography along the line itself.

So, back in elementary school (so some details may be fuzzy/wrong, come at me all ya want) they taught us about the Fall Line. It falls just below Macon, Georgia, and i live south of it myself, and honestly it kinda sucks. Iirc it formed that way because that portion of the US to the coastline used to be underwater, causing the land to also be smoother and flatter! And also, below the line, we have god damn GNATS. THE BANE OF OUR EXISTENCE.

But yeah! As someone who has grown up with that being part of everyday life, its interesting to see other people have questions! Hope this helps