Houdini provides a wide variety of geometry nodes for generating and shaping terrain. These tools represent terrain using 2D volumes where each voxel contains the height of the terrain at that grid point , called height fields. The data passing through a geometry network can contain multiple height fields:

NODE SUMMARY
Heightfield 1st node to start with.
Pattern generating the Pattern like fields.
Noise generating Nose like fields.
Project generating fields from 2nd input and custom geometry.
Blur Blurs the heightfield generated field. It also have different Methods of blurring.
Remap is Remapping the values of heightfields.
Distort distorting the fields and adding different noise details.
Terrace Builds up the terrace looking fields.
Erode Simulates erosion over time. Animation driven.
FlowField
Slump another simulation driven node. But it needs FlowField node to generate Slumps.
Mask Noise generates custom mask Noise.
Mask Blur blurs generated masks.
Mask by Feature masks fields by features, like Slopes, Heights, Curvatures, Direction, Occlusion etc...
Mask by Object makes a mask from the 2nd input object. Can also use Iso Offset node to convert to Fog an to use only insides of the object. which are also blurred.
Cutout using geo to cuts the shape of the heightfield.
Mask Clear clears generated masks.
Resample decimates, lowers the resolution of the created field geometry, voxels.
Visualize can generate specific colors of the layers and masks (nice for texturing)
Layer combines, subtracts etc. two or more heightfields.
Scatter the points onto the generated fields. In the 3rd input we would connect geometry like Trees to be scattered around. In the 2nd input we connect Masks to mask certain areas so that Scatter doesn't scatter there.

SideFX Documentation: [Building terrain with height fields (sidefx.com)](https://www.sidefx.com/docs/houdini/model/heightfields.html#:~:text=Houdini provides a wide variety,can contain multiple height fields.)