Pregenerated planet terrains for random planets. These were in the beta, but had to be cut to fit DA on the GC2 Gold discs.

Using them should improve load times some, and reduce memory usage (especially if you turn down the planet terrain randomness option), since the game doesn't have to generate them from scratch.

Ahh, okay. Thanks Kryo. Kinda big, but if it will improve the performance, Im all for it.

Is this the terrain rendered in 3D from the galaxy map, or the planet surface tiles? Turning the option from 100% to 10% decreased memory usage by over 400MB on a huge map; I'm not sure why it accounts for almost 1/3 of the program's memory usage, as it doesn't seem to be that important to gameplay.

Both. All planets have a heightmap, which is basically a greyscale version of the map on the colony screen (the game uses it to determine terrain types on tiles, and colorizes it based on the class/environment/etc). If the planet doesn't have a custom texture defined, the colorized heightmap is used as the texture on the globes as well.

When you turn the variety slider all the way down, you're basically going from using all of those heightmaps (or if you don't have the package installed, the game generates them at game creation), to just a couple or even one per class, AFAIK. So all planets of each class having the same terrain is the price for the decreased memory use. If you don't care about that, then by all means turn it down to 0.

I've never modded the game before. I downlaoded the heightmaps form stardock, what's the next step or steps? Is this a mod, how do I install it into the game, how do I turn it 0n/off?

Love the game BTW.

It's not a modification, it's a module. All you have to do is install it in SDC and that's it.