You can use either L3DT or World Machine. Creating terrain in L3DT is pretty straight forward; just follow the programs built-in guide on how to use it. once you done fiddling around with the program, export your heightmap in PNG format and add it to your custom level folder that you've created, i.e: levels\<your_custom_map>. Creating terrain in World Machine is a tad complicated to explain, i'd suggest following video guides on how to use it, or find and read the programs documentation. difference between the two is minuscule on how it generates terrain, both programs generate terrain relatively realistic in its most basics. Although World Machine has more bells and whistles into how you apply, control and mold your terrain, making it a more advance program. you can download said programs here https://wiki.beamng.com/L3DT https://www.world-machine.com/ for more further explanation on using L3DT for BeamNG, read this post here (just be cautious since it's a quite out of date guide, but the principle is pretty straight forward))https://www.beamng.com/threads/tuto...or-beam-ng-in-depth-guide-with-pictures.2764/
