What is that imaginary line across the United States on the map?

If you look broadly at a map of the United States, there is a line between North Carolina and Virginia, and between Tennessee and Kentucky, that extends out to between Utah and Arizona. Is there a name for that line? Does it have anything to do with the weather being colder north of it and hotter south of it?What is that imaginary line across the United States on the map?
It's the 38th parallel. It was the boundary for the civil war between the north and south.What is that imaginary line across the United States on the map?
The Mason Dixon line does not follow the the 38th parallel exactly. Oklahoma was a terriroty, not state, during the Civl WarWhat is that imaginary line across the United States on the map?
Has nothing to do with weather, trust me on that! It was just a convenient dividing line when the states were laid out to use longitude and latitude lines. You will notice they are not necessarily straight in some places if you go to close-up maps.
That's just how they're shaped. there really is no meaning.