Back in Gimp I can make a bump map from it, and I can use gradient maps for colors, etc. But I must say, if you have Photoshop, then you should use that for gradient mapping, since it is far superior to Gimp's gradient mapping.
L9.jpg
I have no idea what the scale of this map is, and this is just a quick example, but it is important to remember to cut out the white/land parts and lock the alpha channels and use the 'screen' mode at low opacity. You can blur the edges, fix things, etc later in Gimp/Photoshop.