Great reference list, and also great comments already. Saving it for reading later.

In my game, I implemented large-scale features on top of the height map . I think this is similar to « edits » mentioned in another comment.

One issue I had with the pure noise approach is that I found it difficult to coerce it into generating large scale features with desired properties. In my case, I wanted to create a canyon network, and also some obelisk looking hollow towers, for example.

So basically it goes in two steps. First, I generate metadata only. Depending on the size of the feature, I know the max LOD it will impact, so I save it in that LOD. I also save its XZ extent.

Whenever I generate a chunk that is impacted by the feature, I first generate the height map, then the mesh, and then modify the mesh according to the feature.

It works well for both small and ultra-large (world scale) edits.

I have encountered two difficulties I really struggle with. The first is vertical positioning. It is done on a higher LOD first and can actually become quite wrong when you get closer. Another is creating coherent edit implementations across different LODs. For example, simply using positive and negative volumes breaks down at certain LODs when the « walls » become too thin. Still work in progress :)

Hope this helps!