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Background: this universe has the same physics as our universe. The planet is the same as Earth.

I've drawn out the map of a singular continent and it has all the political modern day boundaries established. How can I work backwards from that to form other continents, tectonic movement, and geographic features of the continent?

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    $\begingroup$ Geographic features form over time scales that dwarf political activity. All of recorded human history is just a blink in the eye to the movement of continents. $\endgroup$ Oct 6, 2021 at 2:09
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    $\begingroup$ The writer is outside time and can work backwards. $\endgroup$
    – Mary
    Oct 6, 2021 at 3:16
  • $\begingroup$ @Mary The writer may be, but there's no way to make a systematic connection between political boundaries and the movement of tectonic plates that a couple of dice wouldn't do just as well. $\endgroup$ Oct 6, 2021 at 11:04
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    $\begingroup$ The movement produces mountains and plains. The effect of those on politics is obvious. $\endgroup$
    – Mary
    Oct 6, 2021 at 12:17
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    $\begingroup$ @Mary There's no way to make some deterministic link between "we have mountains here" and what the OP asks for ( "How can I work backwards from that to form other continents,..." ). If I give you one single frame of a movie, you don't have a way to make the complete movie. If I give you a complete map of California, you can't construct the map of Europe from that. $\endgroup$ Oct 6, 2021 at 16:09

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I feel like this question is relevant to me, because I have a WIP that essentially started with a history-inspired sociopolitical conflict, then I had to reverse-engineer the world to fit that political situation, which I know is basically heresy to a lot of worldbuilders, but yeah, bite me. The main way to keep yourself sane doing that is this:

Be prepared to change the political map.

In my Ancient-Egypt-and-sundry-inspired I-don't-know-what-to-call-it-or-use-it-for-but-am-still-quite-interested-in-it world, I originally had the main source of the Great River be well-known as a lake in a large mountain range, with two cities on either side, but I've since decided that, like its inspiration, the Nile, the river's origin should be unknown to the people of the main area. They occasionally go a certain distance east and then write "Here There be Giants" and go home, because that much land is difficult to traverse without steady food and no such thing as cars, and you don't go upriver as fast as you can downriver. I find that makes more sense and keeps the world feeling more mysterious. And because the world's only city-building races are all in the west, those lake cities, among several others, now retroactively don't exist.

Early Map Concept for the Known World

(I've added, deleted, moved and changed a LOT more stuff since drawing this)

But that's a small detail on the map. The main things haven't changed: a Great River splitting north from south, with its predominant race being thought of by most of the non-river cultures as the villains of history, with the Known World being only a small portion of the actual world as the land and sea are so inaccessible. Those are the things I think are important to the setting.

Only lock yourself in to the details you find most important. If it seems like something would be different based on the geology you figured out, then change it.

I want to stress that it is possible to make a compelling setting working backwards like this. The world I've been talking about started with me designing a simple but diverse lineup of fantasy races for roleplaying based on The Five Races. Then in giving them a place to exist, by taking Egypt and tilting it 90 degrees to the left, I got really invested in the story of the race of Witches, now called Sinis, and their relation to the other humans, of which there was originally one race not counting Half-Giants, but now there are two, the southerners called Gloriens and the northerners called Normishmen. I started with essentially a loosely-imagined political map, then worked backwards, or am still, to make a more concise and complete world, and I do it by being willing to change some things.

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  • $\begingroup$ So should i have started with a geographic map of the world before starting a political map? Would I have better luck with maintaining continuity/believability if I started with a pangea and then worked from there to make currents, mountains,etc? I figured that this would also affect human migration and if the position of continents are not accurate then I can't accurately pinpoint certain political conflicts/phenotypes of the people in certain regions. $\endgroup$
    – alcyone
    Oct 6, 2021 at 16:02
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    $\begingroup$ L.Dutch and Pablo H I think have the answer to that question. Geography influences, but does not absolutely determine modern boundaries, especially if your world has modern technology. Ethnography may be a bit more complicated, but generally just have the people from warmer and drier places like Arabia be a bit browner on average than those from colder or wetter zones like China, keeping in mind that migration events can be unique, for example Indians are most closely related, if I understand correctly, not to the nearest other Asian groups but to Europeans and the Ainu of northern Japan. $\endgroup$ Oct 6, 2021 at 16:38
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    $\begingroup$ Basically, don't worry too much about it. Keep the parts that you think are most important, but just be ready to change everything else. If for example you set up a country's seat of power over Lake X, then realize that Lake Y would have a much greater strategic value, then you can either put the capital on Lake Y, make Lake Y smaller, further away, delete Lake Y, put something more valuable like a rare ore deposit on Lake X, or just have the powers that be arbitrarily decide that Lake X is the capital even though Lake Y has the bigger and potentially more powerful city. $\endgroup$ Oct 6, 2021 at 16:44
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    $\begingroup$ "by taking Egypt and tilting it 90 degrees to the left" <- before the invention of the compass, this was the standard orientation of most maps. Up was considered the direction of the rising sun and down was where it set. Or latter in the medieval period, up was the direction of the Garden of Eden believed to be in Mesopotamia $\endgroup$
    – Nosajimiki
    Oct 6, 2021 at 18:40
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    $\begingroup$ I know, but for convenience's sake, up is magnetic north on my map. $\endgroup$ Oct 6, 2021 at 18:44
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So let’s say your map looks something like this:

A continent with political borders

First, we can place some…

Geographic features

I recommend placing mountains first. Mountain ranges tend to form frontiers between political entities, so add mountains along some of your borders—particularly ones that run roughly parallel to the coasts. Then you can add rivers for some of the other borders. For the sake of the tectonics you want, you might also throw in a rift valley or two and a string of lakes—which are also likely to be found on borders.

A continent with mountains, rivers, and political borders

Voila, geographic features that derive from your political map! Now, based on that, we can consider…

Tectonic movements

Now that you have some mountain ranges, use them to divide up your continent into plates. Some ranges, especially big and broad ones, will be formed by uplifting where two plates collide, like the Himalayas. Others, with more volcanic activity, will be formed where one plate slides under the other (subduction). More volcanoes, and rift valleys with associated lakes, will be found where plates diverge.

A continent with tectonic plates and their movements, plus mountains, rivers, and political borders

Don’t overdo this, though, if you want an Earth-like world. At the continent scale, you have two, maybe three major plates, and one or two minor ones (and if you really drill down, a few microplates around the margins).

Other continents

This one is tricky. There could be anything out there, and trying to extrapolate other continents from the plates of this one is like trying to extrapolate Mars from Earth—sure, technically every atom of Earth is gravitationally influenced by every atom of Mars, and so hypothetically you could determine facts about one from how it influences the other… but it’s not practical.

So instead, go with whatever makes it more interesting. You have a plate that’s driving up into the interior of this continent? It broke off from another continent way back in the mists of geological time. Draw a continent out in the direction this plate came from (then shift the new continent, to account for the fact that it, too, is still moving). Maybe the regions on the smaller plate retain some flora and fauna unlike the rest of your continent, but like those found on the other one. (This suggests barriers, like inland seas or deserts, that have stopped a full interchange of species.)

A continent with two distinct bio-zones, plus mountains, rivers, and political borders

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  • $\begingroup$ One thing to add about mountains is that they either form boundaries or are very far from a boundary, but very rarely just near one. While a Country can hold large pieces of land on either side of a mountain range by functioning as distinct provinces of the same nation. it's harder to hold a small piece of land that is divided off from you. $\endgroup$
    – Nosajimiki
    Oct 6, 2021 at 18:50
  • $\begingroup$ Okay, everyone can stop upvoting my answer, this is the correct one. $\endgroup$ Oct 6, 2021 at 19:15
  • $\begingroup$ @Nosajimiki He does seem to have accounted for both of those scenarios, with that isolated cluster of mountains in the north being in the middle of its country. $\endgroup$ Oct 6, 2021 at 19:15
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Political boundaries are often influenced by geographical features, because they are often convenient for such purpose, like a river, an ocean or a mountain range.

However, the contrary doesn't hold true: geographical features are often the result of centuries or millennia of geological changes, while political borders change in years. Just give a look at Europe: since the times of the Roman Empire its geography is practically unchanged, yet the political border have danced around a lot.

Now you are left with the geographical features of a continent. How do they help you in defining the other continents?

Well, some can indeed help you: for example, a mountain range next to the ocean (like the Andes, or Japan) is an indication of a converging plate border where an oceanic plate is sinking under a continental plate; this implies that from the sea side there shall be a diverging border and an ocean, either existing or in becoming, and those mountain ranges will have quite some volcanic activity. Another example can be that, if a rift split a former unique continent, their margin might be complementary, like South America and Africa.

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Great question! Some ideas:

As @StephenG posted in a comment, geology runs in much larger time scale than people [yours are humans?]. So you might need to run your backwards-simulation in several time scales: human, local features, geology.

Human: history, settlements, migrations, society buildup and change, culture, etc.

"Local features": Rivers change. Forests grow or dwindle. Animals migrate. Volcanos, avalanches, mudflow. Climate change. Changes in predominant winds, in atmosphere structure. Meteorites. Ocean currents. A scale of thousands of years.

Geology: Mountains, plate tectonics, erosion. Planet core. Millions of years.

You could consider each "topic" in turn, think of a plausible reason/explanation/cause, and iterate. Even if you sometimes have to roll dice to choose options (as @StephenG commented), I think you can "run the simulation" backwards, as a change of explanations and causes, causes of causes, and so on.

As @MaddockEmerson wrote, you may need to change your map, for aesthetic reasons, or perhaps because it turns out to be invalid or implausible.

I reckon once you have many "systems" running (climate, geography, ocean, etc.), other continents would appear naturally (;-)) to fill holes in the explanation.

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