Late to the party, but lowland tundra is essentially cold, dry and treeless. In general, it's the name used for such treeless places where the ground is permafrozen a short way below the surface, so shallow lakes and bogs are common, when the topsoil's frost thaws in summer long enough for hardy, low-growing plants to survive. Alpine or mountain tundra is similar, but its treelessness is because of the poor, thin soils, and colder, higher altitude air, as well as general dryness. Lakes and bogs are less common, as the drainage is often better in the higher mountains. It's all downhill from there, after all 😉.

Red desert sands are fine by me too - handy for anyone wanting to recreate Martian landscapes, of course!

If you wanted to add some rails and railcars, Remy did a livestream video on drawing rails and railway rolling-stock here, which may be of use.

It's just a thought, but at this large-scale of map, you can use the straight drawing tool and get a nearly identical "natural" appearance, simply by clicking more nodes as you go along. Although this obviously creates more nodes, they'll end up as a mere fraction of what you'd get by always drawing using the fractal tools, which often add far too many nodes on their default settings. You'll also end up with a map that looks pretty well identical to this, but one that you'll have more control over in all manner of ways.

Sue, I think it may be something on the FOREST sheet. I tried a 1024 px export just now, and it hung for a while before rendering the export on that res. It did create the image, however.

Trying to hide everything but the FOREST sheet also had the program hang for almost a minute.

I've found CC3+ will crash (shuts down) without telling you why if you've set the export to a size your system (or the combined your + CC3+ system) can't handle. Occasionally, you might get an error box telling you something similar before this happens, but not always. Typically, I find setting the antialiasing to zero, or just turning it off, will solve the problem. However, it may be there's something else at work in this case too, of course.