There is no clear front line imo. Obviously the blacks haven't invaded Redania yet since they are still south of the Pontar. On the drawn world map you can see a Nilfgaardian camp at the very southern part of the map so one would assume that everything in between that camp and the Pontar is "neutral" land in which battles have already taken place without clear winners (all still on Temerian soil). That's why it's called No man's land now.
