I did this bass for my best friend.
I painstakingly painted the map from visual references. It would be more accurate had I projected it onto the surface, but I did it freehand instead- not to be some kind of art hero, but because I didn't have a decent projector handy. I do the best with what I've got!!
The process was simply repainting the body; I did a tan / beige base color for the body, then dry brushed leathery highlights on to make it more "mappish." Afterward, the day-long process of painting the map on began- literally spending a whole day sitting and painting. Actually, it was pretty great.
Later on, I decided to spice up the peghead. I did a relief carving of Treebeard and the Ents attacking Orthanc. It's painted in a black gloss resembling Orthanc's exterior.
I thought about buying Lothlorien Leaf clasps to pin on a custom leather strap, but I haven't gotten to that part yet. Maybe for Christmas...