In reply to butteredfrog:
Ortlieb, and I usually work with a Memory Map printout of the area I'm navigating in. If you put it in the A4 document case, you can quarter it so that it fits securely in your hand on a windy day. If you need to, you can stick a 1:50,000 scale printout on one side, and a 1:25,000 scale in the other if you need additional detail of a particular area.
I usually carry an OS or Harvey's map in my bag/with the group as backup.