I spent the last 3 sessions trying to figure out how to properly map a Splatmap onto my terrain coming from WorldMachine. There was always a slight offset that could not be corrected with offsetting the UVs. I finally solved it by using the default landscape size in UE4(613x613), matching the extents in WorldMachine(613mx613m) and the elevation which was 256m to -256m. Now I had a match!
A Splatmap is used to mask and reveal certain materials of the landscape in a natural way. Now that this pipeline is out of the way, I will do a pass on rock assets to scatter around, replace my water plane and probably placing colors on the background mountains. I will next move on to a proper landscape material to begin placeholder textures in Substance.