I've been playing with GIMP, using RobA's fabulous tutorials, and enjoying it very much. I am trying to do a large-scale (continent-plus) map in roughly the style he describes.

I used FT3 to create a very nice heightmap, ranging from high peaks to deep oceans, all exported using flat colors for each level. To select each level, I've just used the "select > color" tool, and have created a layer for each such colored level. Thus I have layers ranging from "Abyss" and "Deeps" to "Peaks" and "Snowcaps." I know, from RobA, how to use any one or more of these to produce masks that can be applied selectively, and so forth.

Now what I want to do is to set a height level, which I believe for land needs to be 0 (low) to 1 (high), with an appropriate number for each layer, and then normalize or smooth or whatever across all of this. Then I can apply a gradient color green, and then do it again only at the higher levels and do it more brown, and so forth.

But somehow, I can't figure out how to achieve this.

I am hoping to use the Bevel or Emboss Distort effect, which (when I've gotten it to work) does produce beautifully sharp-edged high mountain ridges.

I also don't grasp at what point to apply noise if I only want to roughen the textures without significantly altering the heightmap.

Last but not least, I've seen tutorials that suggest ways to impart nice lighting effects to get the mountains to glow as if lit from the northwest, but these are for PS and don't seem to apply very well to GIMP, though I admit that I haven't fought with this part all that much.

Many thanks!

[Note: I'd be happy to upload the FT3-rendered JPEG, but I'm away from my computer on my iPad and don't have access at the moment.]