I just bought some Prismacolor markers to try out putting shadows on overhead line art maps. I've never done that style map before, but I see a lot of potential for being able to add gray toned shading to line art. Here's my first test piece, which I whipped up in an hour or two. (I got impatient on completing the outer wall. Hence the name of the stronghold!)

Click image for larger version. 

Name:	freehand.JPG 
Views:	71 
Size:	2.03 MB 
ID:	87702