Some authors have a truly astonishing talent for making everything in their world fit together in a manner which is logical, consistent, coherent, and follows each element’s consequences all while making everything up as they go and working without a plan. These authors have a rare and enviable talent for seeing how an entire world fits together in their heads while they are inventing random new elements they didn’t know about earlier. These authors are rare.
Authors who think they can do this but actually can’t, on the other hand, are surprisingly common. This isn’t a bad thing, nor does it make those authors who can’t tessellate a world on the fly somehow lesser, it just means that they do need to stop and do a bit of planning before they begin writing. It is, to give a more concrete example, as if one in every million architects can build a structurally sound and beautiful house without having a design (architectural plan, floor plan, etc), without ordering all the building materials they’ll need ahead of time, and without even starting construction on something which touches the ground. Those are crazy genius architects. Most really good architects would never consider doing something that insane and likely to fall apart. Most unwise DIY disasters are caused by people who don’t know what they’re doing and don’t realise they need a plan. The wise architect plans. The wise author plans their world building. But there’s more than one way to plan a world.
Now, typically the main methods of worldbuilding are described as top down (outside-in) and bottom up (inside-out), the former being the creation of a world on the grand scale before moving in to look at the location and characters which will focus in the story and the latter being the focusing on a specific location and set of characters and building the rest of the world out from there. The both have cons, they both have pros, and they both have more variables than the typical division acknowledges.
Starting by building the entire world is a great way to procrastinate while assuring yourself that no, really, you’ll get on to writing your epic work in a few more years once you’ve fleshed out those last few town’s economies on the opposite side of the planet some four thousand years before your story is going to be set. Starting by focusing just on the characters and locations of the plot and making the rest up as needed is a great way to turn your world into a DIY disaster because, chances are, you aren’t a crazy genius architect.
What I’m saying here is that if you are creating a world from scratch you do need to do some planning before you start writing, but it’s probably best to do that planning after you’ve got a basic idea in your head of your main characters and settings. Nevertheless, there are different ways to do that. All of these methods fit into the same basic structure: Step 1; have idea, Step 2; plan world, Step 3; write. When people put world build as step one they never really reach the writing stage. When people put world building after writing they end up with incoherent jumble worlds that only superficially look like they make sense. All of the following methods are different ways of doing STEP 2; PLAN WORLD, and all of them belong firmly between the stages of inspiration and writing.
Start From A Character: So inspiration struck and you’ve decided you’re going to write an epic about the buttoned up princess, her love affair with a hero wielding a great sword, and her epic struggle against the Dark One and now you’re ready to start writing, right? Okay, first things first: back away from the keyboard because (despite a complete lack of individuals titled as such in human history) everyone does “Dark Lord” and “Dark One”. Planning a world based on a character means taking those basic ideas you had and stopping to work out what kind of world would have to exist for those elements to be plausible. That is to say, take every single thing about the idea and note down what it means for the sort of world. Some will be exceedingly unhelpful (buttons have existed since c. 2800BCE, in the Indus Valley region so gives no technological level fix), other apparently obvious but do need to be noted because not all worlds will be the same as ours (princess is a gendered noun so we know the species has males and females as a presumable norm – which is by no means obligatory or default in speculative fiction genres and therefore is worth noting). The world princess has been used, that defines the setting as being a hereditary monarchy, and a bit of research will tell you what sort of cultures and technological levels are required to support such a system (many can, but it becomes a question of which is most likely when combined with other attributes). There is a love interest, which either means that marriage for love is acceptable or that the princess is going to be torn between caring for her feelings and caring for the good of her people, meanwhile the love interest is called a “hero” (that means literary figure renowned for using their ingenuity, bravery, and strength for some greater good) and wields a great sword (is it just an awesome weapon or an actual Great Sword – in which case it’s probably a steel long sword of the kind favoured in the late Middle Ages, found from the 13th to 17th centuries and which would firmly fix the technological level of your world?). Lastly you have a Dark One which implies that your world and culture have the same, near omnipresent, light = good, dark = bad prejudice which is found in the western world.
Starting from a character means analysing like Mr. Sherlock Holmes when he meets a new client. Analyse every part of the character and write down what that means about the world they’re in and you’ll find that much of the world actually builds itself – you just need to map it out, make the history and keep things from contradicting it later.
Start From A Location: So maybe you don’t have any people planned yet. Maybe you just had an amazing dream in which there was a beautiful city of white and pink marble by the sea. Maybe it had high spires glittering and the sun setting behind it, with some mountains between them. It’s the most beautiful place you’ve ever imagined and you absolutely have to write a story about it. Okay, that’s fine, but you still need to plan and extrapolate the world before you can get writing. Despite how it might seem, you can actually tell an awful lot about that world from that brief description – it has a central cathedral, for one, thing, and a cathedral is a Christian church containing the seat of a bishop (which is typically a position of authority or oversight, making this a moderately important religious centre which was given great import when the city was build around it). It’s by the sea, which means that even if the sea is massive enough that they aren’t in contact with the continent on the other end, the people of that city will be sailing up and down their own coast to trade. They’ll also have a focus on seafood, given that most seaside cities develop from fishing villages. If the sun is setting behind it, with mountains between the city and setting sun, the city is either on the eastern coast (the sun is setting behind it in the west, on the other side of the continent) or the city is on a planet which rotates east to west as opposed to west to east as the Earth does. Either the city is obscenely rich from its sea-based trade and can import enough pink and white marble (is that real marble or just called marble by the construction business, which calls any crystalline calcitic rock “marble”?) or, more likely, it brought the marble in from those mountains, which means it has strong connections to mining. That, in turn, will affect what kind of bedrock and surrounding rocks and soils the city is built on, and therefore what grows and how earthquake proof it is. You also need to go back to the image of that location you had and ask yourself if it looked warm or cold (open plan, windows, many gardens, or pointed roofs meant to prevent snow from piling up, etc).
Extrapolation like this will allow you to build up a good idea of what your main location is like, but also what other cultures are in the area and, when you come across some product or resource which would be rare to more than one of them, you can quickly start to fill in the blanks of their history and wars.
Start From Recent History: The key to believable worlds is that history affects what happens later (just like in reality) so if you try to write about some major event without having anything more recent than, say, the dark lord rising to power or the declaration of war between two planets affect it, it’s going to come across as false and cardboard. That would be akin to a world wherein everyone and everything over the age of thirty-five mysteriously vanished from existence, leaving even gaps in people’s memories so that no inherited grudges or prejudices can affect the new squabbles to come (which, frankly, is an interesting idea itself, but runs into the problem that nothing – architecturally, technologically, artfully, etc – could ever be achieved). History is built on cause and effect – and every effect becomes a cause to new effects. This does not mean that a world builder needs to know the entire world history in painstaking detail. It does, however, mean that you need to choose a point in history (preferably several hundred years before) at which point you start your (detailed) history, and paint what comes before in broad strokes which match what else you have created. The point at which to do this is the most major or recent massive change (for example, if you were working with the modern world, you would want to start planning history from the industrial revolution and work step by step to the now, then go back and paint everything from before the industrial revolution in broad strokes). The exception to this is when you are dealing with a story set in the aftermath of some massive, world changing event, in which case you need to work from the previous massive, world changing event so that you know what shockwaves the new change is actually creating and how it has made the world different than your characters remember.
The key here, I should point out, is that you pick a major change in history and work forward from there, as if that point was the start of the world, and every step which follows much make sense given and be built on that point and each step you build away from it. There is, of course, the danger of things not making as much sense as if you had built history from the very start, but it can be mostly neutralised by putting your date of major change far enough back that no one (except maybe immortal beings) is still alive from before it and the world has settled into its new form. This method comes with the benefit of preventing an author from obsessively compiling history as a means of procrastinating.
Start From The Beginning (of The Universe): As I mentioned before, this is the most procrastination inducing method of world building, so unless you’re working on a story in which ancient history or cosmic events are to be of huge relevance, it’s not the best of choices. It can be made more manageable if you work in deliberately broad strokes until you reach a point within a couple of hundred years of your story’s setting, and then begin to work out the history in more detail. In this case you would work out how the universe came to be, when the (or each) planet gained life, then where and when sentient life arose, which groups split off and travelled to settle new lands (and when) and you would make note of roughly when major inventions like the wheel and money turned up, what types of societies formed where, and – of course – who they were in major trade alliances and wars with, when. This is likely to induce self-directed muttering such as “okay so the Soandsos and the Suchandsuches have made peace in the fall of the Whoweretheyagain Empire and one remnant of the empire goes to war with the Soandsos …wait, that won’t work, last time I mentioned them they were trading partners. Okay, so the prince of the Soandsos ran off with the daughter of the governor of the imperial remnant and that sparked a major war – hey, cool, they could be the go-to tragic lovers of that world’s classical literature and be remembered in modern sayings”.
There are two key aspects to successfully using this sort of world building: firstly, you have to restrain yourself from going into detail at every point in history and keep it to manageably broad strokes until you reach things which will be plot relevant and the in-world modern era; and secondly, you have to make sure you stop and ask yourself what the broad results for everyone are each time something happens. This will create a very comprehensive and coherent history, which is good for the author – as it prevents them from putting aging ruins from the wrong culture in the wrong place – but which can be bad for the story as in-universe the people should not have that perfectly correct and accurate an understanding of the history of the world. Real history, to those studying it, tends to be painfully jumbled and the missing pieces get larger the further back you try to figure things out.
Start From A Map: As with beginning from the start of a universe, this method of world building has the double-edged sword of being both extremely good at keeping a universe coherent (assuming the author doesn’t throw a map together with no regard for how geography, geology, and climatology actually work) and extremely good at stalling an author from actually getting any writing done. This is also not the best choice unless you can either draw or use cartography programmes competently. If you’re starting from a map you have to start by deciding what sort of planet (assuming it is a planet or galaxy and not some strange dreamscape) you are dealing with (size, proximity to star, proximity to other planets, number of moons if any and their size, any other oddities to be noted). Then you need to ask yourself about the geological composition of the planet at large, because that will affect a great many things (if you find that one too complicatedly scientific to handle, go with “earth-like”). Now you need to decide on the number of and shape of the continents, based on the appropriate land-to-water ratio for your planet (Earth’s approximately 70% water to 30% land, for instance) so that you don’t make your continents and islands too big or small. Continents don’t perfectly fit together like jigsaw pieces but the general shapes should feel like they almost could – and they should be appropriately spaced so that they could have drifted apart and slammed into each other to form and have been formed by those shapes. Also, if you’re starting from the map, that means that you have to accept whatever currents and weather systems your grand design has caused you (you can’t just remove or shrink something later if you realise there’s no way the described temperate location is not in a rain shadow or should be frozen because there’s no ocean current to warm it from the south, for instance). Now, if you’re world building from a map-starting point then you probably don’t have characters, etc, in your head yet and are likely world building for the sake of world building (which is a perfectly valid thing to do) but if you do have those things in your head and you are struggling with an increasingly nonsensical map in order to make it fit, you might want to try a different method and flesh out the map later.
Once you have the continents in place (and know how much volcanic activity places have, plus a rough estimate of what types of rock are where) and you know how the current affect them and their weather patterns, you need to analyse where mountains, major valleys, rain shadows, and rivers are most likely to be and add them. Beware of being tidy about this – although all of these things need to be in places which make sense, nature isn’t particularly inclined to put things in straight lines or where it’s convenient for people and too many neat rows of mountains will not only strain credibility but snap it. Only once you have these geographical features in place can you start to add things which will be important for when you add sentient habitation. This is the point to work out where rainfall and rivers allow for forests, where the plains are, what areas are lush and which are arid, how far the freeze goes in winter, etc. This is also the point, as it happens, when you need to go back to that information from the start about what kinds of rock were found in abundance where – not only does that affect how plants grow and what kinds of animals will appear, but it also decides what building materials people have and what unlikely locations they might be willing to endure for mineral rewards. Now and only now, is it the time to start placing towns and cities onto the map – based, of course, on where humans would be likely to settle (having water, shelter, and the ability to farm first, then mining communities and the like). Then comes deciding who supports and wars with whom (over what resources are available) and who needs to trade with who (first for survival, then for luxuries). Then comes deciding national borders, as far as such things exist, and zooming in on your map (or creating a paper cut-away) to focus on whichever location on it you find the most interesting and from there to develop culture, characters and plot from the natural constraints of the world you’ve built.
All of these methods of world building have pros and cons and each person has their own preferences among them. But they’re all better than just assuming that you can world build on the fly with no planning whatsoever, because all that leads to is an incoherent mess.