Great job. As I always suggest, use the angle of the ground to determine whether there is just rock (too steep to collect any soil), or whether it's rather flat with grass and trees. That is, of course ontop of the altitude rules.
Thank you! Yes, you are right, yours is the more logical approach. I used it in my bigger ProcGen project (that's where all my procedural generation ideas get thrown in): https://nerokrinion.itch.io/procgen/devlog/465194/diamond-square-island-generato...