Through a discussion on the Cartographer's Guild forums I ran across
a thread about how to make mountains using a program called
Wilbur and thought that it might come in handy for those who like making their own heightmaps for import with
DFHeightmap. The tutorial I linked to includes the creation of rivers, but I think we can leave that to DF. I've included and edited below. You can run rivers if you want (Filter>>Erosion>>Erosion Cycle or either of the other two options if you want to mess with them), but what DF does with that is uncertain, I just did a test and one major waterway ended up mostly ignored with a few small lakes (actually, I think they were the region's oceans).
In Wilbur create an empty map and change the size (Surface>>Size) to 1024x1024. If you have a simple map you wish to add ranges too, File>>Open and import a PNG that has basic areas filled out (water in black, landmasses in white, coastal regions in a dark gray).
Then generate the heighfiled (Filter>>Calculate Heightfield). This opens the Heightfield Computation window. Change the paramters by selecting Ridged Multifractal from the drop-down menu. If using an imported map change Operation to Multiply. Uncheck the Spherical Evaluation box and hit the scaling button. In the surface scaling window select Broken Value from the dropdown menu. Then press OK and watch Wilbur generate the terrain.
Fill the basins (Filter>>Fill>>Fill Basins). Use the default slope value of -1. Next select only the flat areas of the map (Select>>From Terrain>>Flat Areas). Once again use the default values. Then add some percentage noise to these areas (Filter>>Noise>>Percentage Noise). Choose 2 or 3% and press OK. Deselect the flat areas (Select>>Deselect). (Run rivers here)
Change to a grey scale map (Texture>>Grey maps>>Height Map). Then save the map as 16bit.
Open the greyscale map in Gimp. In order to increase the contrast and make the elevation effects stand out more it is necessary spread the grey map over the full range of black to white. To do this open the levels window (Colors>>Levels).
You'll want to drag the black and white level markers towards the middle to be near the edges of the black area on the histogram.
Save out as another file, it should drop down to 8bit grayscale. If not, it doesn't really matter.
Import this file into DFHeightmap as elevation, tweak as necessary the parameters (an offset of 70 to 90 with default ratio should work fine). Import your other maps (or not) and save to world_gen.txt.
Run and generate a new world.