1) create an interesting world in DF with advanced features.
[I use an x variance of 600, a y variance of 900, 1000 erosion cycles, and a weighted mesh for elevation. This produces more or less monolithic "shield volcano like" island regions. I use the "large island" as the base parameter set, and then spice it.]
2) export elevation, vegetation, hydrosphere, and biome maps from legends mode for that world.
These will be very large bitmap files, and it takes awhile to generate them. Some of the maps, like vegetation, are black and white heatmaps depicting vegitation density.
3) in paint.net, I open the height map (the one that also records underwater elevations), then rotate the hue by -72 then convert to greyscale. This makes the "blue" underwater elevation pixels into teal, which then more or less seamlessly blends with the rest of the heightmap.
4) combine the other maps into a colorized vertex color map using translucent color layers over the vegetation map.
5) use photoshop to convert the heightmap into a 16bit/channel greyscale image, then use a blur filter to soften the gradiations over the improved bit depth. Save it as a 1 channel 16bit raw file with no header, IBM byte order, noninterleaved.
5) process with tesannwyn (a 3rd party utility for importing heightmaps and terrain for bethesda games) use the 16bit raw for the elevation data, and the colorful combined veg, biome, and moisture map as the vertex color map.
6) load the resulting plugin file with the creation kit, and use the now colorcoded ground to place trees, grasses, plants, rocks and other features.
7) clear the vertex color map using the creation kit's terrain editing abilities, and put tastier looking texture data down using the skyrim default texture libraries.
generate LOD data
9) play on it!