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GameMastery Guide / Creating a World / The Cosmos

Creating Your Planet

Source GameMastery Guide pg. 164
The first question every GM should ask about a world is whether or not it’s a planet. This is by no means a foregone conclusion—planets are a relatively recent concept, and in the millennia before Earth’s shape was proved, various cultures had widely varying theories. Many believed that the Earth was flat, a disc floating in an endless ocean or supported on the back of an elephant (in turn riding on a huge turtle). Others believed the world was square, the slopes of an enormous mountain, or bound by the roots of a colossal tree that held up the sky. Who’s to say that any of these isn’t true for your world? Perhaps your setting is a giant mobius strip, or a facet on the many-sided gem of the universe. You’re the GM, and what you say goes.

That said, however, creating a world so wildly different from our own can capture players’ imaginations and raise questions that you’d rather gloss over. If your world is flat, how far away is the edge? Can you fall off, and what keeps the ocean in place? Who lives on the flip side, and is it possible to dig a tunnel through to them? As with everything in this section, the farther you stray from the Earth standard, the harder you have to work to maintain your players’ confidence.

Yet even using Earth as a model, there are still several factors you should take into consideration.

Size: For many GMs, the temptation when designing a planet is to make it larger than Earth, the better to increase the mystery and provide unlimited canvas. Yet this carries problems both logistical and physical: If your planet is larger than Earth, does its gravitational pull get stronger? Your horizon will also be much farther away than ours—how does it affect your siege adventure if the defenders can watch the raiders approaching for a week? Even on Earth, it took a long time for the various regional cultures to expand and make contact—if distances double or triple on your world, what does that do to social demographics or political relations? Do the various populations and ecosystems of your world even interact?

Composition: What your planet’s made of is important. For instance, if your planet is hollow and full of dinosaurs, what does that do to its gravity? How do volcanoes work if the planet’s core isn’t molten? What keeps the seas from draining into large-scale networks of caverns and tunnels? A planet’s composition is also important to its magnetic fields and thus to navigation—if compasses don’t point north, what do they point to? A city of wizards? A guiding star? God?

Movement: Does your planet rotate, and if so, how long are your days? How long is 1 year (meaning a single orbit around the sun)—or does your planet revolve around the sun at all? Perhaps the crystalline spheres of the ancient geocentric model are literal truth in your world.

Moons: Earth’s moon is responsible for its tides—if your world has no moon, does it still have tidal action to stir its oceans? What about lycanthropy or other magic inherently tied to the moon? Conversely, if your world has an enormous moon or multiple satellites, do you have enormous and erratic shifts in your tides? Are the moons close enough to reach, and what effects do they exert on each other? Are they lifeless rocks or thriving worlds?

Archives of Nethys

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Creating Your Planet