So I hoped to enter this months challenge. Working with a bunch of maps in the same style seemed an invitation to scripting so I dashed off write a gimp script to take a map template like this:
Click image for larger version. 

Name:	template.png 
Views:	680 
Size:	7.4 KB 
ID:	6018

and running the script creates a map like this:
Click image for larger version. 

Name:	output.png 
Views:	404 
Size:	581.5 KB 
ID:	6019

It works, but I'm still playing with the script and doubt I'll be able to make a token set for the map, unless I just crib from by clip art (which is what I would do for my self).

One thing to note is that the output has been cropped in by one grid on all sides, a step that was necessary to allow connecting tunnels and shading to work cleanly at the edges, but I'm still not happy about it...

-Rob A>