New info after additional testing
I created a brand new ‘creative’ save to do some further testing. Only one new Base was created and initialised, for which I made a backup to be able to compare as a clean state.
First I wanted to see if a ‘floor’ would have data saved in the ‘TerrainEditData’ when not resulting in changes to the terrain. I placed a wall on the surface, with another on top, to then place a floor snapped to the top end of the top wall. No data was generated at all. Then lower the floor to snap in between, basically at a single wall height. Once again, no data was generated at all. Once placed at the bottom, snapped against the bottom of the wall, resulting in flattening the terrain, new data was generated with about 9 entries in the ‘Edits’ sub array.
Next test was to see if removing this floor piece with entries in the save, would remove the data. Sadly enough, no changes were made to the data at all, keeping any entries it had created.
Now I could test if placing the floor back in the exact same spot would result in a new set of entries. I had previously snapped the floor, so getting it in the exact position again, by once more snapping, was not too difficult. I was happy to see it had not generated new entries. It basically used the previously created data instead. So removing a building part is not clearing the data that comes with it, but then replacing with the same building part in the exact same location, does not create its own new entries, but using what is already there.
Now to see if using a different part would result in new entries, even when in the same location of the removed floor. Sadly enough it does create new entries, but depends on the part used. I noticed that a large floor part, uses the same data as 4 small floor tiles, in this case. This makes some sense, as 4 small floor parts, has the same volume/area as a single large floor part.
Now wanted to test if deleting the base would remove the entries in ‘TerrainEditData’. So I placed several more floor parts, to be able to see a clear difference in the Terrain Edit limit indicator. Then deleted the base to check the save file. The base is removed from PersistentPlayerBases, as it should. However, the ‘TerrainEditData’ remains unchanged.
Now I could check if creating a new base elsewhere, would start with the same ‘limit’ already present, even though the previous base no longer exists. Well, … sadly enough, the limit for Terrain Edits, starts off where you left it. So it already includes the edits made with the first base, which has been deleted. The data is still there, so as expected, you get a jump start on the limit from any deleted bases.
Now I wanted to figure out what the actual Terrain Edit Limit is. How many edits can be made to the terrain before reaching this limit? A single floor parts usually result in 9 entries in the ‘Edits’ part, when just flattening already reasonably flat terrain. Placing a floor basically makes it sink in just a tiny bit, leveling the terrain below to be smooth. However, when placing floors this way, I didn’t see the limit indicator move fast enough. I did however notice how at some point, terrain did not get removed for some odd reason. I had not even reached the limit yet! Apparently some terrain does not allow removal at all. To be honest, I had so far not experienced this yet, possibly having to do with the latest update.
It would have taken me quite a while before reaching the limit, so instead I decided to use Cuboid Rooms. I placed one on top the terrain with a door, then placed another below and went from there. Each Cuboid Room I placed, now forced a maximal change to the terrain, being just below the surface, each basically resulting in 16 entries in ‘Edits’ I have not counted how many Cuboid Rooms I placed, but I went another level deeper and had to make it quite large. I saved just before reaching the limit on the indicator, then started adding more Cuboid Rooms until it showed the limit was reached. Reloaded the save, to then stop just before the next Cuboid Room would reach the limit. Then I placed a few small floor parts at the surface to actually reach the limit and check the saved data. The amount of entries should now be as close to the limit as possible.
The result of having reached the Terrain Edit Limit for this base, had a total count of 10,001 ‘Edits’. Knowing the following:
- Each underground Cuboid Room resulted in about 16 ‘Edits’
- 1 Cuboid Room I started with having 4 ‘Edits’
- 3 small floors to reach the limit, likely 4 ‘Edits’ each.
Maybe I should have actually counted, but I assume I used 625 Cuboid Rooms total (including the one above ground). The limit in amount of ‘Edits’ is however obvious, basically 10k, where the last part that makes it reach the limit is fully ‘saved’, resulting in just 1 edit over 10k (10,001).
The total amount of ‘Edits’ that can actually be stored is exactly 15,000. I therefor assume the remaining 5k is the limit for Terrain Manipulator edits. This of course considering previous research with TM edits being stored in the same location.
Now I wanted to verify once more, if previous findings would still be the case. So I tried to build another base and see if I would have a new limit or not. The answer is a clear NO! You start with the limit already reached with the first base. Reloading or restarting the game makes no difference.
Does deleting the base that reached the Terrain Edit Limit, remove all the stored data? Once again, a clear NO! The base entry is removed to no longer exist, but the ‘TerrainEditData’ remains unchanged!
A big gaping hole was left though, almost certain to be filled in with terrain again over time. Oh and just after adding below image, I just noticed the Base Computer located right next to the hole at the bottom. The image was taken right after deleting the base. At the time, I had not noticed the ‘new’ Base Computer. Make note of that position, I will explain a bit more below.
The Base Computer, was actually placed right on top the Save Point before removing the base. I had taken the above image and moved away to create a new, but still empty base about 641u away. After seeing the Terrain Edit Limit for this new base was already reached, I walked back to the first, now empty base. Only then did I notice a Base Computer down below in the hole left. Now seeing it in the previous image, makes it even weirder, as in the image I took after return, has the Base Computer in a different spot even.
The Base Computer did show interaction, either ‘Claim Base’ or ‘Leave’. No option or way to delete it however. I never even placed it there in the first place!
Not being able to remove it anyway, I decided to do a last test. I flew to space, to warp to a new system, to check a Space Station for teleports. So I did, with the teleporter in this new system, only showing the new empty base. The first base which was deleted, did not show as an option to teleport to. I teleported back and walked back over to the old, now removed base, to see the Base Computer gone. No idea what that was all about. It freaked me out a bit, even more so now, considering I had not even noticed how it had moved another time before I found out.
Lastly, the image below to show the terrain already growing back.
Below an image of terrain that would not get removed at all. Similar to the terrain that could not be removed by the floors either (second image in this post). Of course you can see this being the case in the big gaping hole that was left as well. Not sure what that is all about…
To conclude:
Any terrain edits caused by building parts, will never be removed. Not even by deleting your base! The only solution is to use a save editor, knowing the format and how data is related (indexed).
Awaiting the promised solution Hello Games is trying to come up with 
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oh well, guess I’ll just have to build a bunch more 
