I've only just thought of this idea but being able to do such a thing on a computer would be really, really useful (to me anyway!).
What sort of software would be good at drawing routes and adding location information to a scanned map? I guess the gimp could do it but are there any applications more specifically for this sort of thing? Ideally the additions would be in their own layers so one could look at only the 'nice bridleways' or the 'good horse accomodation' additions. It would also be nice to be able to add notes to marked locations.