The Bones of Earth: Creating Maps

[Jubal]

The Bones of Earth: Creating Maps
By Jubal

I originally wrote most of this post for the now-defunct Exilian Academy a few years ago, but figured it could also sit here and get a new set of readers: it's simply a brief overview for setting designers, be you writers or game devs, looking at how to make realistic feeling earth-like geography. A lot of this is really about re-applying basic observations of our own reality, and working out the underlying rules that make them make sense and look right for our readers & players. At some point I may repost the follow-up article for worlds with geography very unlike our own, but even for most of those this should be useful.

A Planet's Bones: Plate Tectonics

This is an awfully high school teacher way of looking at things, but the old adage that a planet is kind of like an onion and has layers is actually pretty useful for a fantasy setting designer. The reason our Earth is the way it is and has the geography it does has a lot to do with the way it is made up - and so this leads us on to plate tectonics.

Our planet is made up of big plates of rock, floating on a molten core of magma (Note: it's magma under the surface, lava when over the surface). The plate boundaries are shown above. So why is this important? The seas and mountains we have are often determined by where the plates are, and so it's by understanding this system that we can work out what's going to look right in terms of our own maps.

The basic thing to take away from this is that any really big mountains, any earthquake zones, and most volcanoes have to occur on a plate boundary or former plate boundary. (I say most volcanoes; Hawaii is in the middle of the Pacific plate where some magma has forced its way through the crust, but due to the volcano basically just being a hole through which some magma pours there isn't much in terms of internal pressure.)

Secondly, plate boundaries go in lines. This is why it looks kind of weird if you try and make a mountain range that's just perfectly circular with mountains in the middle and hills around the edge; imagine taking a piece of paper or cloth, putting your hands flat on the edges, and then pushing it together. That's what the earth is doing, and so you need to make it look like that's what's happened. This certainly doesn't mean you should try and map out all the plate boundaries in your world (though feel free to): if your world is of as old an age as our own there will in any case be plenty of mountain ranges that no longer have active plate boundaries next to them. The key thing is to think in natural lines.

A related feature to note is that peninsular regions are often bounded by mountains (India with the Himalayas, Italy the Alps, Iberia the Pyrenees) - this is because the peninsula is slowly shoving itself into the continent nearby. Mountains along shorelines are common, too, as a dense oceanic plate pushes itself down beneath (the Andes and Rockies fall into this category).

A Planet's Bloodstream: The Water System

Tectonics are one of the two major factors in land formations; the other is water.  Water, in its various forms, has huge effects on the land around it. The three main forms of water we need to worry about are the river, the ocean or lake, and the glacier.

Rivers are always a key feature. The only really important thing to remember is that water flows downhill, and so any land area can be divided into "river basins" where all the water is heading for one river. Not all rivers have to start in the mountains, but many do; if your river flows in a direction other than towards the sea or a large lake without an obvious natural obstacle, it will look pretty darn odd. The edge of a river basin is called the watershed; watersheds can be important features in themselves, for example between the Waveney and Little Ouse River sources in the UK lies a thin watershed which is the only land bridge between Norfolk and the rest of England. Rivers are also notable in that they cause erosion and have different formations in different places; in the plains a river is likely to be deep, wide, and meandering, in the mountains it will be straight and fast-flowing, cutting out a steep-sided valley or gorge. The ends of rivers tend to have wide estuaries or deltas; putting a river going at right angles across the coast into the sea tends to look odd, particularly for large or major ones.

Oceans and lakes are important parts of any map. The first vital thing to note is that they are not standalone features; any major body of water must be fed by rivers and streams. Secondly, the rules of gravity still apply; a lake is likely to be at the bottom of a basin of rivers, or along a route to the sea where the way out is only thin (and so the water backs up into a lake). Coastlines are often a more difficult thing to work on, but do not need to be inherently difficult; remembering indentations where the estuaries and mouths of rivers are helps, as does noting that coastlines are rarely straight. They tend to be formed of bays with jutting headlands between them – harder rock forms headlands, softer soils and rocks will be eroded to make bays.

Glaciers are the last thing to note. When visiting many mountain ranges, you will see that they valleys are not as steep as you might expect if a fast flowing but thin river or stream had cut them. Huge U-shaped valleys are more likely the result of long-melted glaciers, huge walls of ice rolling down. These will also have deposited rocks not native to the local area (moraine) and formed canoe-shaped hills pointing in the direction of the glacier (drumlins). This characteristic set of features is common particularly in northern Europe or mountain regions since the ice ages, and remembering these can help add some realism to your features.

An Example: A Look at Middle-earth

If you take a look at a map of Middle-earth:

You can note a lot of the above features, and that's interesting for one particular reason - plate tectonics was barely known as a theory when this map was drawn! It nevertheless roughly follows a fair number of the rules that plate tectonics explains (even if one can pick apart the details) simply because these are what gives the map its earth-like feel.

Examples include the long lines of mountains; the Ered Luin are good candidates for being on a current plate boundary, and all of the ranges generally fit together well in naturally flowing lines and curves (the right-angle over the Anduin where the Ered Nimrais meet the Ered Duath is odd, but not impossibly so). Note the water basin inside Mordor due to the Ered Duath and Ered Lithui; the water flows inland and therefore has to form the Sea of Nurnen. The river Lune in Eriador is an excellent example of a river basin lying between two sets of hills; the lake above the falls of Rauros shows how the water would have backed up before breaking through in the famous waterfall formation. The Brandywine, Greyflood and Isen all have large and visible estuaries rather than going into the sea at right angles, and note the large delta at the mouths of the Anduin.

Whilst it's possible to get these features right just from guesswork and a gut feel of how maps should look, it's certainly helpful to have these basic geographical features in mind when working out the shape of your world. I hope you've found this helpful - now get out there and get world-building!