These are all good questions. I've given it a bit of thought but, from the perspective of the civilized populace, the lowlands are very much a mystery. That's "Here There Be Dragons (and Mist Demons)" territory.
The fog is effected by tides a bit as well as weather patterns. I'd say that the lea of the mountains might be a bit safer in some areas but altitude is the primary safety feature from the toxins of The Mist. There are definitely low lying areas that can get swamped by The Mists when there is bad weather at "high tide". These areas are analagous to places like Florida or the Gulf Coast of the US where the coastline doesn't provide much protection against rising water.Is the poison fog Windblown? If so are spaces in the lea of mountains safer?
The exact origins of The Mist are unknown.Is it generated by lowlands ? In which case are the leading edges of islands safer?
To be honest, I've not quite decided. Some friends I've been talking the idea over with have posed the idea that The Mist is a by-product of the use of Arcane Magic and that the rise of an empire of Wizards of late (who have solved the problem of transport by way of magical portals) is causing The Mist to rise.
One thing I should clarify about The Mist: It's not like cyanide gas or anything quite so dangerous. It is toxic over long periods and exposure for even a day is enough for weaker individuals to become sick. Eventually (in as short as a few days) it can be fatal. But exposure to small doses over a long period can also cause memory loss and mutation. And of course there is the hazard of the Mist Demons who can't live for long periods outside The Mist. (some think that the Mist Demons are humanoids who became mutated by The Mist - they may be right)
Yeah, I'd considered this as well. So far my answer is that the humid Mists of the lowlands cause the area to get a larger than average amount of rainfall. The flatter, larger plateaus have some sizable lakes (and some AMAZING waterfalls off the edges!). In places where water tends not to collect so easily, the inhabitants have dug large cisterns inside the mountains and plateaus. All that and a little GM handwaving makes the world habitable.If this is all mountainous - how do they deal with water? Often, not a lot of land around a mountain that's usable. Plateau's can be limited or very far apart....
Me too man.Just trying to work out the wrinkles in my own head....
Sigurd