[Steven Lake]

Originally Posted by AndrewH

Why is it necessary to say that it's a 'large world'? Even with 2/3 our planet covered with water, Earth still has about 150,000,000 sq km of land. The United States, the third largest country in the world, only covers 6% of that. If I'm not mistaken, about 90% of the earth's land surface is still undeveloped.

That's actually an excellent point. In fact, on a couple of occasions I've actually increased the land mass of the planet where 70-90% of it was land and the rest was water. However, the planet had just as much water as Earth has. The way I did that was to have vast quantities of the water stored underground in massive caverns filled with water. Sorta like natural storage tanks. The hydrological cycle worked just the same, however the water covered less of the total surface.

Which really, given the physics of water movement around the planet, including humidity, even if only 10% of the water was on the surface, you'd still have the same levels of humidity and the same types of weather, because the percentage of water in the air vs what's on the planet as a whole is minuscule. The average humidity around the world is about 60%. If you take that and do all the crazy math that goes with it (I'll spare you the algebra lesson) it accounts for about 0.001% of all the water on the planet.

So even with only 10% of the surface area covered in water, you could still maintain normal humidity levels in the air, and thus normal weather patterns such as what we see here on Earth. And yes, I'm nerd enough to have researched all this. Mostly because when I write sci-fi, I want it as scientifically accurate as I can where and when it's needed.

Originally Posted by Elfwreck

You can have vast, epic battles and huge unexplored regions on a planet 1/3 the size of ours. Especially if there's no fast travel like trains or airplanes. If most people are limited to ~30 miles/day, an expanse of a thousand miles is huge.

Agreed.

Earth still has vast, unexplored regions. Most of them are covered by ice. You probably need ice caps; you don't need the largest continents to be the coldest ones.

Again I agree. Case in point. I have one planet where I needed to do three continents for the series, and I have cooler northern regions, hotter southern regions, equatorial areas, islands, prairies, mountains, deserts, etc. Every planet will have a variety of environments on it, and if yours doesn't, things get a little awkward. Of course, as you pointed out, people with limited travel speed will see small geographical areas as massive.

The amount of metals *on the surface* and the density of rock that people have access to, doesn't necessarily directly connect to how much metal is under the crust. (Well. It sort of does, but you'd need to provide a lot more details than the average fantasy novel gives, for a geologist to be able to draw any conclusions about that. Having a lot more gold & gems than medieval Europe had floating around says absolutely nothing about the planet's composition.)

Excellent point! There's also something else people fail to consider. Gravity is inversely proportional to mass. The more heavy elements you have, the heavier the gravity will be. Why do you think Jupiter can be 11 times more massive than Earth and yet have only 2.5x's the gravity of Earth? It's because Jupiter has no heavy metals. The heaviest known elements in Jupiter's atmosphere are helium (10%) and hydrogen (90%) and given that we have elements as dense as plutonium on our planet, plus a massive sphere or iron at the planet's core, our gravity is naturally heavier.

If you go to Mars, our nearest neighbor, which is slightly over half the size of Earth, it has only about 1/3rd our gravity, and the only reason it has that is because of the very high iron and lead content on the planet. (it's not called the "red" planet for nothing) So there are a lot of factors that affect the gravity of a planet. The best thing to do in cases like that is simply to go with my first suggestion and avoid really getting into the details of the size, gravity, etc of the planet.

To the OP: As you can see, I do tons of research on any of the planets I write about, but even then less than 1% of the details that I work up on a planet go into the actual story. The primary reason for such detailed research is that I know what the boundaries are of the planet/environment I'm writing about and what I can and can't get away with. For example, if someone's living on a mars sized planet that has earth level gravity, they better sure as heck have a massive amount of heavy elements to make up for the extra gravity that would be required to create Earth like conditions. The inverse is true with larger than Earth planets, where heavy elements would have to be much, much rarer to allow for a lower than typical (ie, earth like) gravity.