A plain old pencil, sheesh, now why couldn't I think of that? Just tried it on one of my maps and it seemed to work fine.
Do grease pencils have a fine enough tip for actually writing on a map rather than just marking areas?
I think all my fine tipped Sharpies have dried up. I'll have to get a fresh one and try that out too.
I save my maps both for reference (during and after trip) and as trip mementos. If whitewater is involved I write the rapid classifications (ahead of time if I can get them or my estimates as I encounter them during the trip) as well as portages that aren't in what seems like the obvious place. During the trip I mark down where I camped each night and again mark portages that I've found that don't seem to be in the logical place; or that differ from my pre-trip research. I also jot down areas that look like they might have good camping or areas that look to be devoid of camp sites as I pass them.
My trips are usually long and I often come back on the same route. I've learned that I can forget a lot in 3 weeks so being able to look at the map to see the location of odd portages, known camp sites, and just as importantly to see where I should avoid looking for camp sites, comes in handy. After the trip I have these marked-up maps to rekindle my memories and since I'm not opposed to repeating part, or all, of a route in the future I'll have those notes to reference.
Alan