How can I lower the landscape equally into the ground?

[PikaDERP]

In the image above, I built an open mine pit on the surface from the bottom to the top, however I’ve reached the height ceiling of landmass and can’t expand further. This was a bit of an oversight on my part, and I’ve been trying to figure out a way to lower it into the ground.

One method I thought would work was selecting each cell (Landscape>Manage>Select) and manually lowering its Z axis. This however leaves gaps between the edges, and the surface is still “programmed” as if it never moved in the first place (As seen below, for an example)

Is there a reliable way for me to achieve what I’m trying to do?

Cheers.

[UnrealVerseGuru]

o/
Beside playing with landscape sculpting tools you can export heightmap and manually edit height with fav image editing tool, e.g. Gimp
You can either paint more white/black or use some adjustment layer on region you need to flatten
I found it way faster to edit global changes, like Z height, and this essentially is your problem

[MostHost_LA]

You can move the landscape tiles up and down and not have a gap, but you need to do so programmatically.

Once your tile has reached 65535 value you start the next tile at 65535/2 height.
Then 0 will have the value of the height where the previous tile ended.

Obviously, because the highest value possible in 16bit is Odd, you may just want to limit the landscape to 65534 and do the same with even numbers. Which is where the “programmatically” comes in.

This is useful to have higher “per meter” detail and avoid stepping on really tall landscape (think K2 from below sea level to top).

With that in mind.
Your solution may be as simple as exporting all heightmaps and starting a new terrain with a different Z scale.

Ofc, if the heighmap doesn’t get adjusted you will distort the terrain.
Chanches are you can just move your current terrain downwards and extend the vertical unused portion avaliable to the terrain by manipulating the data directly in GIS.

If you let a gis program keep the height values as they need to be and rebase the lowest point you cna pull this off quite easily.

If your terrain was not a properly formatted png16 file, you will have to do extra work.

You start by taking the current scale, and the documentarion provided ratio, and calculating your max heigh/lowest point to then rebase your normalized heightmaps in GIS without causing distortion.

From then, you just rebase the lowest point…

Absolutely do not ever do as @UnrealVerseGuru suggests.
Most programs do not natively support 16bit and will distort the values of the heightmap - often causing stair stepping since you go from 65535 possible values to 255.

Heightmaps are data sets, not graphics. You have to work with them in programs that can properly manipulate their data in order to prevent unrestorable corruption.
(Once you go down to only 255 levels and save you can toss the file. There is no recovering the lost detail).