Of course, not all sci-fi is set in some exotic offworld location, or even on a far-future Earth, but when your story calls for something futuristic, here are some ideas.
Earth … but not as we know it
Even if you pitch your story many thousands of years in the future, you can expect the continents on Earth to look much the same, but surface conditions might be vastly different from what we know today.
On a warmed planet, sea level rise might have altered coastal outlines a bit or a lot depending on the level. Alternatively, intervening factors might have resulted in runaway cooling and a new ice age. A changed climate might have other effects, such as extreme or unpredictable weather – heat, cold, storms, flooding… Places that are inhabited today may be deserted in the future, and vice-versa.
Human presence could be very different. We’re used to towns and cities surrounded by farmland, and regions of forest, desert and wilderness. A future world might be war-ravaged, radioactive, poisoned, or a garden idyll. Cities might be elegant pictures of 1950s utopian optimism, or dystopian concrete or metal jungles. The balance between urban and rural might be radically different, the world built over in an endless conurbation or urban centers few and far between.
Other worlds
The most obvious away-from-Earth setting is another planet. With such a blank slate, there’s a lot to play with. Is its surface habitable or not? If yes, then all the above questions about surface conditions apply. Otherwise, what conditions make the planet uninhabitable? Atmosphere absent or unbreathable, or maybe dense and high pressure. Extreme temperatures. Extreme weather. Radiation. Unpredictable seismic or volcanic activity. Maybe no solid surface. High gravity. Hostile local fauna or flora, or riddled with active pathogens. For a workable story setting, any of these factors will need solutions to keep fragile humans alive.
Other characteristics of the world might profoundly affect the story, making life for people more difficult or maybe negating a difficulty. What if the planet’s rotation is markedly different from Earth’s? Very short or very long days, all the way up to a tidally-locked arrangement with the sun giving perpetual daylight to one side and night to the other. Similar consideration to the year, though this needs to be thought through more carefully to be consistent with the sun’s mass and heat output. How about the inclination of the planet’s axis? Our 23-degree slant gives us our seasons, but what if it’s much less (a seasonless world) or all the way to a 90-degree inclination? During the course of a year, the sun would be directly overhead at one pole and then the other.
Other surface conditions to consider: Surface water (a lot or a little), geography (mountains, deserts etc.), geology (maybe metal-rich or metal-poor), surface temperature from a faint star maintained by internal heat more than solar radiation.
Pretty much any aspect of the world we know can be played with to good effect. A couple of cautions: First, think things through. This is more important for harder sci-fi but it helps if your fictional world pays homage to known science and obeys some self-consistency. For example, a very Earth-like planet depends not just on size, composition and distance from its sun, but also on a suitable biosphere. The former is easy to imagine happening by chance, the latter merits some explanation in your worldbuilding. Second, try to give your world color by avoiding unbelievable uniformity. Having the world entirely covered by desert or forest or endless undulating grass is easy, but also not very credible, boring, and (worst of all) lazy worldbuilding.
Straying away from planet-sized bodies able to retain an atmosphere – including large moons of larger planets – smaller bodies offer possibilities and their own challenges. Small moons and asteroids don’t have the gravity to retain a breathable atmosphere, so habitation would need to be enclosed, or atmosphere held in by other technological means. On the surface, or underground, possibly in caverns or tunnel systems either natural or artificial. Not all such bodies are stable chunks of rock. A body that’s more of a loose aggregate would pose its own challenges and risks. Or what about a solid mountain-sized chunk of ice in a far-flung orbit?
Locations for bodies like this include the obvious moon of a planet, or part of an asteroid belt surrounding the sun. These seem to be the standard picks. But your setting could be part of a farther-out and more dispersed cloud of orbiting rocks, or sitting in the dust in one of the Lagrange points of a large planet, or wandering free and dark between the stars.
Of course, if you’re talking about a small world, you are also talking about low gravity unless you use a technological fix. Even worlds with low but noticeable gravity (such as that on our moon) will impact movements we take for granted. For example, you can’t easily break into a run, and once you’re moving it can be hard to stop, as astronauts on the moon discovered.
Artificial worlds
Many sci-fi stories take place in or on entirely artificial settings, which come in a wide variety of forms. Mostly these are either “fixed” or mobile, though in space nothing is really fixed. The distinction in my mind is whether or not the structure is intended for travel.
Fixed structures include things like stations orbiting a planet, moon, or star, or drifting free between stars. Pretty much the same as natural bodies. Kinds of installations include passenger terminals, military outposts, scientific observatories, ore processing factories, shipyards, trading posts.
When you talk about a space station, typical pictures involve collections of spheres, cylinders, rings and other shapes assembled into some coherent structure. Is it neat and orderly with clean symmetrical lines, or some messier structure like the ISS, all the way to random agglomerations of modules stuck together like barnacles on a rock?
Beyond typical stations, even those measuring in the kilometers across, there are more exotic possibilities for even larger habitats. The simplest, and easily scalable, is a pair of flat plates on the ends of a spindle like a set of barbells. Set it spinning about the mid point of the spindle and you have gravity. Rate of spin will depend on the size of the structure, but we can easily be talking about country- or continent- sized plates. This concept can be expanded to a full ring, which lets you do away with the spindle. One of the main points of this arrangement is to set it almost edge-on to the sun and arrange for a day-long rotation. This gives you both gravity and a natural day-night cycle.
Then you can go really big, and build a ring that encircles the sun. This would be a breathtaking engineering feat, and also introduces new challenges. The obvious one is back to day/night, which Larry Niven solved with the inner ring of shadow squares. The more subtle one is stability. Keeping a spinning structure centered on the sun needs active management because it’s inherently unstable. But just think of the living space!
Reining things in a little, you don’t need to limit yourself to simple geometry. For example, your habitat could be more like a spiders web of structures strung together over a vast volume of space. You are only limited by your own imagination.
Mobile settings
The obvious mobile setting is some kind of ship. Ships include things like military, merchant, passenger and exploration craft, and a lot of the same considerations apply to them as to other artificial structures. The big addition is the need for propulsion and whatever constraints that imposes. Space flight is covered separately as that’s a big topic in its own right. Depending on your technology, propulsion might place limits or other requirements on things like size, shape, and configuration.
Other kinds of structures might fall into the “mobile” category without being as freely-mobile as a typical ship. For example, a lot of stories take place on generation ships – large self-contained structures embarked on long multi-generation voyages. The need to be fully self-sufficient for this length of time places additional requirements on the vessel.
An extreme example of this line of thinking appears in Larry Niven’s Ringworld series, where the Puppeteers took flight with a whole constellation of worlds flying in formation.
Common considerations
One question common to most of these environments, other than full-sized planets, is gravity. Even though some constructions are truly vast, they typically don’t come big enough for their mass alone to provide a decent gravity field. That leaves you with questions: Zero (or micro) gravity needs no technological solution and could have interesting story consequences. The downside is that it makes a lot of natural movements impossible and you have to think things through for practically every aspect of your characters’ lives.
Alternatives to produce artificial gravity include spinning all or part of the structure, which poses interesting engineering challenges, or maintaining a steady acceleration to give the illusion of weight. Harder sci-fi tends to favor these kinds of solutions that work within known physics. Softer space opera is more likely to duck the issue and the constant attention to detail by invoking some form of artificial gravity. That has the benefit of letting you get on with the story in a more natural way.
Another question that applies throughout, particularly to artificial settings, is the look and feel of the place. This is part of the general “atmosphere” discussion, but the appearance of your physical surroundings will do a lot to set the tone. Do your interiors feel cramped or spacious, clean or grimy, tidy or cluttered, luxurious or spartan? Are you going for the Death Star vibe of polished surfaces and lighting designed to be imposing, or the lived-in down-at-heel feel of the Millennium Falcon? Military or civilian? Do you want to surprise your reader or lull them with familiarity?
When figuring out how your setting appears to the characters, it’s not just the visual aspects – space and configuration, color and lighting – that matter. What about the other senses? Distinctive odors, heat or cold, humidity, sound … all these will help flesh out the setting and help you convey a rich environment to your readers.
Ian S. Bott, Writer and artist 