In Borneo in the 60s we were issued with maps that were the result of aerial survey. Where there was cloud when the picture was taken, quite often, the blank space would be labelled ‘Relief Data Incomplete’. The middle of this is where you usually wanted to go. You would blunder off the printed bit of paper DR-ing to a cross that somebody else had marked on blank bit of your map. There would be the occasional surprise like a river or a mountain range but the most important thing was to know the way home. The trick here was to do periodic 360 turns so that that you had an idea of what the scenery looked like when you coming back.