The entire workflow:

• Part 1: Download elevation data as an image, preparations (editing)
• Part 2: Generate a terrain from texture (WorldMachine)
• Part 3: Modify the terrain in WorldMachine
• Part 4: Generate the additional textures from the modified terrain in Substance Painter/Substance Designer
• Part 5: Create the scene in Maya/Arnold

Part 2: Generating a terrain from a texture in WorldMachine

• After you downloaded the Tiff file (from https://gdex.cr.usgs.gov/gdex/) you have to fix the one pixel wide (or high) column (or row) additional pixels (sometime you have both a column and a row) with an image editing software.
• You might want to adjust the width/height ratio of the image to correct the distortion of the map. (You can change the ratio later in WorldMachine as well.)

In WorldMachine:

• Delete all the default nodes
• Create a File Input node
  Generator -> File Input
  Double click to open
  
  • Load the texture
  • Set the Width and Height values (of course this is an approximation)
    Width (in km) = 30 × width of the image (in px) / 1000
    Height (in km) = 30 × height of the image (in px) / 1000

    

  • Set the Altitude Scaling to Specific elevation range
  • Set the Elevation Span:
    First value = Data Value Min from the texture output data
    Second value = Data Value Max from the texture output data
• Project settings (World Extend and Resolution)
  
  • Turn on Allow non-square extends
  • Set the Width and Height attributes (same as in the File Input node)
  • Set the Normal Build Resolution (you can change this later to get more detail)
  • Go to the General Setup tab and set the Maximum Elevation and Base Elevation attributes (Same as the Max and Min values)
    
• Set a water level and click the Show button.
• Click the Build button
• Change to 3D view (F8) to see the generated terrain preview
• This is a fairly accurate representation of the real terrain.
• You can change the colors of the terrain: Set Terrain Color… button, or you can turn off the colors and use the shade option only.

Cheers, D