In the UK the three compass points are on OS maps, sometimes with the changes predicted for multiple years. The older the map the less useful it is. You then h

In the UK the three compass points are on OS maps, sometimes with the changes predicted for multiple years. The older the map the less useful it is. You then have metal in the local rocks which can cause problems. Terrain recognition is far easier, there is far more error correction built in, but if you are hit by a patch of fog and visibility is down in to 30m (let alone 3m!) you need dead reckoning. Trouble is even a 1 degree error can turn into significant errors after a very short distance.