Hi,
imo you need a bunch of devices for navigation. Depending on the situation I am using a compass, GPS or an altimeter. If you are just walking, a compass and a map are enough. If you are stuck in a white out, navigation with a GPS is more reliable than using a compass and helps you out of the situation. And if you are on the way up to a mountain, the altitude is a more precise way to predict where you are and if you should consider to turn around than any other method.

Alex