This documentation is written with TerreSculptor 2.0 in mind, but the same principles apply to other software.
You can get TerreSculptor 2.0 for free and it’s a fantastic tool for creating landscapes. There’s also a ton of support for Unreal Engine so a good fit if you’re using that. Get 2.0 here:
Via the homepage you can get access to a bunch of freebies which include a RGBAK material setup for Unreal Engine, which colorizes parts of the landscape based on a splatmap.
Using a splatmap we can color specific parts of the terrain using data from our terrain generation software. This is nice because auto-materials generally have a much higher performance cost.
However, keep in mind that manual adjusting of the terrain is a bit of a hassle, requiring you to export your edited terrain from UE back to TerreSculptor, regenerate the splatmaps, and export again.
TerreSculptor RGBAK Splatmap Creation
TerreSculptor UE4 Splatmap Landscape Workflow