I'm currently planning for my own new story, and in one point in time there will be a city somewhere on the Atlantic Ocean which has to have the space resources necessary to sustain for around 1 billion people, the survivors of a global catastrophe. There is no possibility for people to live elsewhere, as this city (which has no final name yet) is the only safe place. How should the city be designed in terms of housing, growing food, transportation and overall look of the city to support that much people in the smallest volume possible without lowering the live standards below basic levels (everyone has food, water, a place to sleep and some entertainment)?

  • Assume current technology, or technology which comes likely in the next decade, with a few exceptions: every basic work, including growing food and maintaining every part of the city can be done by robots. You have no energy problems, because if you need more power you build more fusion reactors (which are completely safe in this universe). Also you have super strong and super light building materials, so building structures which are 4 km tall is no problem.

  • The whole city should be air-locked. There should be no damages or deaths if the city was suddenly transported to a vacuum. So it has to clean it's own air if the atmosphere is not available.

  • Government is a dictatorship of a single long-living trans-human, which controls every system of the city and cannot be removed. Assume this dictator does only good and will do no harm.

  • Population can be controlled by contraceptives in the food and water. The inhabitants have no control over this.

  • The city should not be impacted by tsunamis, storms or freak waves.

  • There don't have to be enough ships, planes or other means of transport to the land, because leaving the city is not intended.

  • Water and air have to be cleaned of bacteria and viruses, because there exists very harmful types with could infect the whole city. There exists a 100% reliable test for such pathogens, but no cure, so every infected has to be burned.

PS: Please be gentle, I have been following Worldbuilding SE for quite a while now, but this is my first question :)

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    $\begingroup$ Welcome to Worldbuilding! Have you had a look at these posts? They might be of some value to you: What would be the practical considerations for a floating city always at day? and Can airborne floating/flying islands be scientifically possible? $\endgroup$
    – T3 H40
    Commented Apr 3, 2016 at 12:06
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    $\begingroup$ About the size of India? $\endgroup$
    – JDługosz
    Commented Apr 3, 2016 at 15:03
  • $\begingroup$ Welcome to the site. Can your 'city,' be disbursed into multiple cities, with spaces in between urban areas (like a country: a billion is a lot to fit in just one urban growth boundary)? Cheers for the clarification; I'll take a stab at it. $\endgroup$
    – Mikey
    Commented Apr 3, 2016 at 16:48
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    $\begingroup$ @JDługosz I was thinking the same thing; Good luck fitting China into a single city xP $\endgroup$
    – minseong
    Commented Apr 3, 2016 at 20:22
  • $\begingroup$ Does your city need to be large enough to prevent its inhabitants from becoming motion sick? Some people get violently seasick, even on cruise ships in the middle of the ocean. $\endgroup$
    – Marion
    Commented Apr 3, 2016 at 22:06

3 Answers 3


Very Large Floating Structures is an active field of Research and Development. There are quite a few experiments such as the Mega Float in Tokyo bay (a country used to natural disasters such as the ones mentioned by you).

Mega Float Tokyo Bay

The technology seems feasible and stable although some of your requirements are though to follow. I doubt a structure of this size would be able to do well in vacuum. It's not just about full isolation from outside but also about pressure difference. In the sea the biggest pressure would be exterior (so it floats), in the vacuum would be interior.

For the current state of this technology I would advise documents such as the following:

Very Large Floating Structures: Applications, Research and Development

Having one billion people inside is hard to achieve since it would necessarily be crowded. In any case I think a modular approach to such a construction would be the best one deal with all the characteristics you've mentioned (so several constructions connected by bridges or tubes, etc.). Each module could have it's own specifications on temperature, humidity, hull strength, and so on. For a current use of this technology today check, for example, Assembly of the International Space Station:

Mockup of assembly of ISS

As for survival in a closed environment I would suggest taking a look at concepts such as Close Ecological System such as Biosphere 2:

Biosphere 2

Obviously you would need to tackle each of the problems on a one by one basis (after all no such project exists) but using current technology I think you can explain most of your structure if you follow good architecture and engineering principles.

  • $\begingroup$ Your comments bring to mind Starship UK from Doctor Who, though it would only contain ~59 million people by current population figures. $\endgroup$
    – Marion
    Commented Apr 3, 2016 at 22:13

A floating city possible would by using a material with an incredibly strong electric field able to float a city in the sky but this way your citizens would not be able to use anything made of metal because it would be destroyed almost instantly and the city has to be made of an incredibly light material ,because the heavier is the city the stronger the electric field must be to support it's floating and if the field is too strong it could kill people due to the iron in their blood

About purifying water from viruses the easiest and cheapest way is to simply boil all the water to 1000 Celsius degrees in order to kill every single virus in it , then get the Vapour and cool it down to liquid state in a clean container while all the dead bacteria and viruses will be left in the container where water was first boiled


I correct myself , there's also another option but I'm not really sure about it, it's called Aerogel or also known as solid Air , I know it's lighter than air and can support x1250 times its weight remaining at the same height but due to its incredibly lightness it would be transported by the winds

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    $\begingroup$ Floating (on the ocean), not flying! Aerogel is not lighter than air: the air part of the foam is air, and the rock part is heavier. $\endgroup$
    – JDługosz
    Commented Apr 3, 2016 at 15:07

Here is a city all floating in China. enter image description here

I would imagine like solar farms that are on water it would have to be calm water most of the year to work.

enter image description here


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