How to to create orbital landscapes

Greetings,

I’m currently trying to do a model of a Ringworld inspired by the image below:

The Greebles aren’t much of an issue, I’ve done that using Discombobulator, but the water and terrain presents a serious challenge. Any ideas how I might do that?

Use a tiling image generated from a texture of the earth. Mask out the water and add a high gloss value to it. Add slight bump to the texture and there you have it.

How would I mask out the water? RGB to BW?