Alright, here's another small question
Is it possible, in any way, to view the area of Skyrim in the Tamriel worldspace, in the Heighmap editor? Because by default, only central Cyrodiil is visible.

A quick answer would be appreciated

I don't think you can view Skyrim because I don't think it even exists in-game. I think that everything you can see of Skyrim from the border is probably just dummy LOD that doesn't actually have a heightmap. Might be wrong though.

navigate to heightmap editor / view ..then click regenerate overwiew

open and enlarge the overwiew window...you will notice a yellow square...this square can be moved (by leftclicking on the overwiew map)

the area covered by the yellow square will be shown in your heightmap editor window

cheers

Thanks it worked!
Now, after making huge landmass edits, saving-time in increased a lot, I have to wait for about a minutre or so every time I save. Now what's the best way to bypass that? I was thinking that maybe creating all major landmass edits along with possible region generation first, and live with the long save-time, and then either do the fine tuning on a new esp file which is dependent on the other esp. Or perhaps convert the original esp to a master... what's best?
I'm currently just messing around with the "create huge landmass" methods to get a feel for it, so I'd be glad to have some tips

depends on the worldspace....if your new landmass is in its own worldspace you can create an esm ...if you are working in the tamriel ws I would recommend to create a file just containing the heightmap and then use this esp as a master by esmifying it with wrye bash...if you have heightmap data and region data in one file pathgrid generation will kill you....the pathgrid generator always saves after genearting a few cells ( don't know exactly after how much cells)....this can take days for a big file :brokencomputer:

So its best to esmify it, then create like, one esp for regions, one for pathgrid etc, depending on the files they need... and then merge it?