Terrain Builder heightmap.

[BuitreX 0]

Question, how can I lower the altitude of a real map in asc format. I have a real map with an altitude of 800 to 2400 mtrs, and I want to reduce its altitude by 800 mtrs to put a lake. tnk. BTRX.

[RoF 239]

Use L3DT > heightmap > change vertical range

 

If you just change Average Altitude, it shifts the sea level up or down.
Changing just Altitude Range will squish or stretch the total range (but keep the other ratios where they were).
Changing just % above Sea Level will shift the total range up or down.

 

So in your case you would do the first one