It's either 1\4 or 1\2 a sector from the edge of the map and you get your arrow saying you are off the map. That is probably up to now all the investment in it Hitech is willing to go. That arrow follows your location pointing at you I believe, so it's not like you are invisible once you pass the boundary edge of the clipboard map. I make all the area outside of my 10x10 arena water and boarder the 10x10 with a continuous highland or mountain range. That way you cannot come back in at water level NOE, and it keeps you exposed to radar and 163.