Average altitude (DM parameter)
The 'average altitude' slider in the design map parameters wizard determines the average height of the terrain, and consequently the fraction of land above sea-level.
This is demonstrated below, where where I've made terrain with average altitude settings from 0% up to 100%:
| Average altitude | Design map | Heightfield/Water map | 3D render |
|---|---|---|---|
| 0% (left, sea) |  |  |  |
| 25% |  |  |  |
| 50% (center) |  |  |  |
| 75% (default) |  |  |  |
| 100% (right, land) |  |  |  |