A Map Reading Skill Primer

You don't even have to mark them, assuming the map has the features of the land on them.

Humans are the easiest to spot, all their borders are straight lines, no thought to the land, they want exactness, whatever the price.

The Elves, they follow the rivers, the edges of forests, if the border is all curves, it's Elven land.

The Dwarves, they can catch up an amateur, but once you learn how to recognize mineral deposit indicators you're fine.

And of course, anything hastily marked in red is land that's fallen to the Hellspawn. I suppose that's technically easiest.