It makes most sense that it is a natural end of rampant urbanization, but could a truly planetary city ever come into existence without the direct control of a single organizing body? If so, why would they decide that such a completely developed planet is best route for whatever their goals may be? If not, would the cost/difficulties/drawbacks of remaining/expanding on the burgeoning city-planet drive independent owners away? Is there any situation in which a single-city planet would be the logical development aside from the rule of extreme cool?

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    $\begingroup$ Asimov's "Trantor" was such a World - one big city $\endgroup$
    – whytheq
    Commented Oct 2, 2014 at 10:37
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    $\begingroup$ As was Coruscant. Reading Foundation lead me to ask this question. Well, these four. $\endgroup$
    – neph
    Commented Oct 2, 2014 at 13:24
  • $\begingroup$ It may not technically be a planet, but Ravnica from the Magic the Gathering Multiverse is also a world entirely occupied by one city. $\endgroup$
    – M.Herzkamp
    Commented Apr 20, 2015 at 13:46

5 Answers 5


Lots of questions, but I'll try to answer:

Forming without a Ruling Body

A completely urbanized planet might be able to form without one ruling body. This would mean that the different countries on the planet would have to be very trusting of each other. Or at a point in war where you couldn't destroy each other's cities.

In the Middle Ages, France and England were at war. Along one river in France, each country would build a castle, each on their own side of the river. Around these castles towns would form, the two enemy towns may be very near each, even though they were at war. Cities on an urbanized planet could form similarly. Even if both countries were at war, the cities could come up to the boundary line (or very close) if the technology or incentive was there not to attack. In the case of France and England, the river prevented a quick attack on the opposing town, meaning that the town would have time to flee to the castle and be protected.

If the two countries were allies, then they might not object to building cities right up against each other. There would probably be a small boundary line, but this would be negligible to the size of the city. It might even be used as a park.

Why Such a Planet is Good

Cities provide great opportunities. They are the sources of jobs, because the jobs can find labor. They are the source of government, because the governors need a place to meet. If cities kept growing, with bigger corporations and bigger amounts of work, it could be economically beneficial. It might also be more efficient (more people in a smaller space), keeping scientists together so research could go on. It could also be politically useful, everyone in one place is easier to manage than having them scattered across the stars.

These are all reasons to do this if you had the ability to travel to other habital planets. If you couldn't travel, a planet-wide city would merely provide you with enough space to house all your people.

I don't see why there couldn't still be private landowners, it is just likely that a land owner would get a "cubic" plot, meaning that their land doesn't necessarily go up into the sky forever. This would make it easier to build large sky scrapers.


Your final section of the question asks why this could happen. I believe I have already answered that, but I will summarize.

Such a planet might exist if there were a single government and the population needed a planet-wide city to provide enough space. Or it could exist if the government thought a large city to be economically or politically beneficial.

Such a planet might exist if there were multiple governments and they were at peace. Each government would extend its city as far as possible, for the reasons above. Or if the planets were at war, a system were each side couldn't attack the other would allow for the reasons above to take over.


There really isn't a sound economic reason to create a city-planet. People need food, they need air and they need a place to put their waste. And while there are certainly ways to mitigate those needs without breaking the urban environment, they can't be fully taken care of that way. Not to mention the sheer vast expense; you have to cut down every forest, you need to flatten the tallest mountains, drain the oceans and fill the deepest ravines. And you need to build factories to replace the important functions all of those things perform.

All of that is theoretically workable, but in order to sustain the population, you must clearly have space elevators or some other technology to lift vast amounts of material or personnel in and out of orbit. You must clearly have the ability to build vast space stations or to terraform other planets in the system to grow all of your food and dispose of your organic waste without entirely wasting it. You must clearly have the technology to survive in great comfort somewhere besides the clearly overcrowded and ludicrously expensive big city. It might be cheaper and more effective to just telecommute from your station in low earth orbit and fly a shuttle down when you need to be somewhere in person.

Add to this that the main reason that people typically want to live in cities, that things will be close by to you, works less well on a planet-wide scale and the whole thing looks rather unfeasible. Living in space is just much, much cheaper. Religious or cultural reasons could maybe explain it, but it would require something fairly specific, strong, and well-tailored.


"Could a truly planetary city ever come into existence without the direct control of a single organizing body?"

I think you would need some sort of governing, which is true of any city or country. In this case, it's possible that the planetary city could have started as multiple independent cities who each grew gigantically large. These "sub-cities" may still rule their own areas. However, there'd probably need to be some sort of organization to coordinate everything - possibly like the United Nations.

"If so, why would they decide that such a completely developed planet is best route for whatever their goals may be?"

Most cities grow naturally, and presumably this one would too. I doubt that anyone would decide, "Hey, let's turn the entire planet into an entire city!" What's more likely is that due to increased population and demand for land, the cities would slowly come to dominate the world.

Obviously, food production would be an issue. Food would either have to be imported from other planets (feasibility would depend on the transportation technology) or grown under factory like conditions in giant (underground?) warehouses using growth lights and genetic engineering.

If the city planet is part of a universal planetary system with ease of transportation, then it's likely that it could specialize in the sorts of goods and services that cities offer. It'd probably be a hub for many major industries.

"If not, would the cost/difficulties/drawbacks of remaining/expanding on the burgeoning city-planet drive independent owners away?"

I think this would depend on the goals as well as the costs. Depending on the technology of your set up, you could create it a number of different ways. For instance, if the city imports it's food from elsewhere, farmers would obviously migrate to other planets.

Food would probably cost more, though, again, this depends on technology. Food grown under factory conditions might still be cheap. Habitable or desirable land would probably also become costly, and other people may find a greater quality of life on other planets (like some people know move from the city to the suburbs).

"Is there any situation in which a single-city planet would be the logical development aside from the rule of extreme cool?"

For a human civilization, I think the city would have to part of a large and efficient trading network. I don't know that it'd be logical for the entire planet to be a city. There's bound to be high mountains or deserts or tundra that's simply uninhabitable.

For an alien situation, you could change the meaning of what we understand as "city." Maybe the aliens use organic life forms to construct their buildings, or maybe they all live underground and grow crops on the surface.


An urbanised world could happen many ways- extreme war pollutes the whole world but remaining civilisations have high resources stores- especially energy. There is no better to handle radioactive land than building over it- solid concrete is an excellent barrier. Aero- and hydroponics (and industry) expand over the world by simple necessity.

Extreme Green governments lock up big swathes of land for nature and the other countries' people respond by uncontrolled urban-sprawl. The Green government collapse by starvation and the people and industries keep the sprawl going. Its sort of happening now. Needs a vast population to need to cover the world or most of the world locked up by ocean.

This will need vast amounts of cheap energy and resources but as long you have the cheap energy then resources is not a problem- the Earth has vast amounts of aluminium and silicon in the crust- we'd just draw the resources from the ground. It would have vast amounts of waste heat. The pre-existing condition of cheap energy is the only thing that go against having independent/local owners as it need lots of money to get the economies of scale to produce. It would only limit it to many significant corporations to produce the energy- if those corporations aren't into excessive control preferring wanton demand instead then there isn't anything stopping the whole world being segmented. A whole urbanised world is the thing that one large government (authoritarian) wants- its so unwieldy. It was for a long time very difficult for large empires to have central control. China is as big as it gets and its not really centralised- its really multiple governments. Russia is of course bigger but its less nominally authoritarian than China. The Chinese government doesn't really China to be bigger- the parts might big enough to threaten the nominal central government.

  • $\begingroup$ Hey, welcome to the site! You have some good ideas in the answer, but you may want to try and work harder to answer the actual questions asked in the answer. The asker has some specific things he wants to know. See if you can answer those questions too. $\endgroup$
    – DonyorM
    Commented Oct 2, 2014 at 8:27

I think that a city-planet would be hard to come up with as a solitary idea and convince different nations/worlds to cooperate in building it, since it would most likely be such a huge undertaking, it would have no precedent. Trading and travelling can be done without a huge construct like that, so there would be no reason to come up with the idea. However, people didn't come up with the idea of building each major city in history, it pretty much happens cumulatively.

A possible, in my opinion, origin for such a city-planet would be one that circumvents the need for deliberate planning and cooperation, such as the following:

In the beginning there was trade

You have multiple worlds across lots of star systems with interstellar travel fast and practical enough for trade and casual travel (much like Star Wars, which had Coruscant). There are various space bases and trading posts across intermediate star systems, orbiting planets usually but sometimes oribiting the local star directly, due to practicality or choice by the owner to build it there.

Trade routes pass more often through certain systems than others. In fact, at some relatively distant point in the past, most routes go through a specific star system with multiple bases due to how much trade and travel goes through it. The system is so popular because it stands between large clusters of star systems and thus it forms a convenient trade route to other large clusters due to low amounts of celestial bodies (asteroid fields etc.) and is the safe and common path for trade. The popularity of this system as a trade node and passage point attracts trade through itself from neighboring systems and alternative routes.

Everyone puts their eggs in one basket

As time goes on, the bases are going to naturally grow and expand - they might be privately owned and operated or operated by states, but it's irrelevant - their holders compete to attract more trade and travel through their own station/base. Some people work there, so there's some dwelling accomodations. Trade cooperation happens and some bases decide to merge for mutual profit - smaller owners can't compete, so they merge to stay in the market, larger owners subsidize trade through them and welcome the new additions to their own base, which gives them more capacity and a share of the profits of others.

Considering that there's lots of different worlds moving in and out and a lot of transactions happening, as the bases coagulate into a single main one, there is political and social interest in regulating it. If it is such an important node to the entirety of a huge number of star systems and worlds, there is mutual interest to keep it running and grow it. So it grows in the same way as before. Private owners attach their own expansions, some for dwellings, some for shops, some for products, others for depots and craft maintenance. To keep everyone satisfied, a sort of representative body is established to handle administrative matters. Due to social structures on the worlds using the station, a cellular political structure, based on voting and station section hierarchies is established.

The biggest space bar in the universe

The station grows, until it is so massive, it's the size of a small moon. Give it a few thousand years and in the intermediate time, it has been slowly moved out of its parent planet's orbit (if it orbited a planet in the first place) and is now as big as an earth-like planet, orbiting the star of the system. It becomes the center of political and economical matters since it is effectively neutral ground and all trade routes go through it (or most at least). People are born and die on it, it has enough mass to have regular gravity on its surface (although by this point, generating and regulating gravity technologically is probably to be expected) and it is, for all practical purposes, considered a planet.

Have you been reading the funny pages again kid?

Assuming you have multiple worlds across multiple systems, the material isn't hard to find if there is enough mining. You don't need to strip planets clean - there's lots of ore and metals available on space rocks, clustered conveniently in asteroid fields. A bit of this from all the systems would easily allow for enough high quality material and mass to create a planet-sized body. And there you have it: Coruscant :P

Noone needed to come up with it - it just happens given time, fast enough travel and enough star systems with their own trade structure. It has a hybrid government to manage it, slowly growing out of small practical needs. It was never the best idea out of many - it's just the best option now, since it's already there.


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