The surface layer is based on Megascans that can be blended further with other assets or with other stack layers such as liquid layer, paint layer etc to create the desired look for your project.
The Atlas layer consists of real world scanned assets from the Megascans library that serve as decals which can be mixed or blended with all other layer types bringing forth endless possibilities while texturing.
Surface and atlas layers have these properties:
Blending is one of the core tools to combine two layers to create a custom Mix.
Placement allows you to place your layer on the base layer according to your requirements by using any of the three available placement modes: Freeform, Box Tiling or Projection.
Height Frequency controls only come up with Surface layer and Atlas/Decal Layer.
High Frequency: Control the intensity of the finer details of the surface.
Low Frequency: Control the intensity of the larger details of the surface.
Threshold: Determines what is considered high and low frequencies in the displacement and normal map. If you set it to a low value, more frequencies will get controlled by the Low Frequency slider. If you set it to a high value, more frequencies get controlled by the High Frequencies slider.
The Solid layer also has channel-specific controls that determines its look and feel. See Channel-Specific Controls for more information.