The first thing I remember learning about geology was that gravity was always in charge. This was way back in grade school and we were given the impossible task of making water run up hill in model water system. Our teacher was a great believer in hands on learning, and also, I think, had a cruel streak that enjoyed watching us get frustrated when we couldn’t complete the task assigned. In this case it took us all of about fifteen minutes before every group had given up. Then we got the lecture about how the water system worked. He pointed out that somehow the water had to get back up into the clouds so that it could fall as rain and sent us home that day with the assignment to figure out how that was possible.
As second graders, we weren’t all that bound by the limitations of the real world. So we came up with all kinds of methods for getting the water back up there. Most of which involved some kind of pump or other mechanical device. When we got back the next day, the teacher had set up a solar model with a 100 watt bulb heating the water in a terrarium and collecting the vapor in a flask. How magical it all seemed when he explained that water could only flow down hill, but water vapor was like air which could be pushed up if there was heavier air to take it’s place.
Whenever I’m designing a map for a new world, I always think of that silly experiment we tried so hard to complete back in second grade. Water, just plain can’t flow up hill – not as water. So when I’m trying to figure out where the rivers go I know that I have to start them in the mountains and let them flow down to the sea. If I want a river to dive into the sea from the top of a great cliff, I have to make sure that the water never had a chance to go down somewhere else. Not such a difficult problem if you start with that simple premise.
Build the mountains first, then the rivers flowing down any which way they can until the carve their paths into the rocks. The rivers will tell you where to put your cities and towns. From there you can map out your highway systems. You can even figure out where the lakes are (those places where there is an up in all directions – then the water can’t go anywhere because it is stubborn about that downhill thing).
Figuring weather patterns is only a little more difficult. On Earth, most major weather patterns (the big ones that decide where the storms go) move from West to East. I forget all the mechanisms that go into this, but it has to do with the rotation of the Earth. Since it usually doesn’t matter much, I assume that all planets follow a similar pattern. That means that air coming off the pacific ocean will pick up a lot of water down near ocean level where it is relatively warm and then head up into the rocky mountains and get cold. Cold air can’t hold as much water vapor, so it falls as rain on the Western side of the mountains. Then when the air comes back down the Eastern side of the mountain it is dry. That means that most deserts are East of mountains.
Major storms tend to follow a similar pattern. On land they are ruled by the jet stream and are pulled along that trajectory. As the jet stream migrates North and South with the seasons, so do the storm tracks. Season also dictate the kinds of storms you get. There really is such a thing as tornado season and hurricane season. I’d have to do a lot more research that I want to right now to tell you when they are, but that’s not the point here. They follow a pattern. That pattern is something that your people will be used to and ready for – in the same way that the people in Kansas and Oklahoma just live with the tornadoes or that people in the the tropical rain forest expect the rain at noon everyday. The folks along the Southern East coast and Golf of Mexico should by now know what to do when a hurricane is coming.
That’s where all of this is going. There are some places on Earth where it is easier for people to live and other places where it’s more difficult. There are places where it makes more sense to be nomadic. Even the local foods will be determined by the weather, which will be determined by the mountains. All of this just from trying to decide where the rivers go.
Map building is a fun exercise for me. Even in my fantasy stories it brings me back to the science that I love. It reminds me that sometimes the stuff we learn in elementary school is still important.