The CPL syllabus requires more folding and re-folding of maps than I thought was possible - and if you turn up for a nav lesson with a beautiful map all nicely squared and clipped together in all the right places, you can GUARANTEE that the instructor will divert you to somewhere on the inaccessible other side. My map was such a mess after the training that I had to buy a new one for test day. Instructor mentioned some kind of concertina method, which would work nicely if the 'height' of the map was 8 inches, but I never sussed out how to concertina, in a cockpit, something that is 3 feet high.
Have printed off the instructions kindly provided by rustle.