Hello, everyone--I haven't been in this fine forum in quite awhile, but I came across a series of Photoshop brushes that I immediately thought would be useful for some of you folks:

Here's the link: http://leichnam.deviantart.com/gallery/

This person has a bunch of brush packs for "old books" that would work for maps; plus some neat "decay" brushes for aging the parchment of your maps.

Enjoy, and keep on drawing!