I've been working, on-and-off, on a massive map for an existing fantasy setting. By combining every printed map (blown up to the largest scale published) and then drawing over them on separate layers I have created a great composite map. I plan to take the terrain layers and make a height map and then blend in the terrain textures to produce the final map.

This thing is BIG. Over 40,000 pixels wide. Photoshop requires that it be saved as a .psb Large File Format file, instead of the normal .psd. After reducing it in scale, it would print out as 8 feet wide and 4 1/2 feet tall on a vinyl banner.

Progress so far:
Coasts are drawn.
Land/Sea alpha mask is created.
Mountain, Rough/Tall Hills, and Hills are each blacked out in separate layers to work as masks.
Forest, Deserts, Marsh/Swamp and areas of Grasslands in the wastes are also separately blacked out.
Rivers are drawn as decreasing [double 9pt lines, 9pt, 6pt, 3pt lines] on a single layer.

I have worked out a technique in which I set the range for Clouds/Difference Clouds by pinning the filter between the grayscale tones at the thresholds I have selected for each hill/mountain type. I need to fine tune this still, so it produces shapes that more closely specify the terrain type. Right now, I'm thinking about putting in a texture map for each layer, at a low opacity, that shapes this noise. What I want to avoid doing is drawing each set of ridgelines for every mountain range, across an entire continent. Ugh.

My hope is that I can make a master height field to pass to Wilbur so I can get a nice erode going over the weekend. And then use this better height field to shade the flora-terrain textures, which would then could either become a displacement layer or a light highlighting layer, or something.

Obviously I'm never going to be able to show a WIP for a 400MB grayscale TIFF, but I may post portions in the future.

What I'm looking for at this point is suggestions on how to progress. Either feedback on the process I suggest above, or people pointing out other techniques I might try for improved appearance.