Oh. The thing to remember with that map is that each of the squares is a 300 x 300 block.
The wiki entry on Mars breaks down the exact range for each sector.
A good rule of thumb is that the lower your coordinates, the closer you are to the center of the game map, the higher the closer to the edge. If either side of your current coords is over 300 then you have reached the outer perimeter. If either of them are over 600 you have run off the map and will see darkness in your radar.