The opening chapters of Asimov's Foundation characterize Trantor as being a dense, highly-populated city, to the point that it's almost exclusively indoors and extends a mile underground.

But in the Encyclopedia Galactica entry on Trantor, Asimov states that Trantor has a land surface area of 75,000,000 square miles and a population over 40 billion. That works out to a population density of 534 people per square mile, no more dense than a small town.

Is there anything to account for the metropolitan, honeycombed structure of Trantor even though it has such a small population density?

EDIT: This question has a comment noting the population density and Asimov's later revision to Trantor's numbers, but it also states that it doesn't fully make up for the discrepancies.

  • 3
    Most of the space is taken up by all the humongous computers you need to administer the galaxy.
    – user14111
    Mar 27, 2016 at 23:37
  • Possible duplicate of Why is Trantor, from Asimov's Foundation, all underground?
    – Valorum
    Mar 28, 2016 at 0:09
  • A comment on that question does give some further details on Trantor's population density, though this stands as a separate question from the original.
    – exupero
    Mar 28, 2016 at 0:34
  • I know nothing about this, but maybe he meant floor area. The other thing that occurs is the logistics challenge of provisioning such a large city. Maybe the additional space is required for transport purposes
    – user67228
    Jun 8, 2016 at 0:17
  • The whole planet is covered by the city, so they must have huge spaces full of crops, the underground seas which they use to grow algae, etc etc All that taking a lot of space I suppose
    – max pnj
    Jun 8, 2016 at 12:35

2 Answers 2


Well, this area has to hold, apart from living people:

  • working facilities (an small town will have many jobs "outside" in the fields), including all of the imperial bureaucracy.

  • other facilities like hospitals, universities, schools, army barracks.

  • industry and food processing factories (and probably nobody wants to be in the immediate neighborhood of those), storage space.

  • spaceports for getting the ships from 50 agricultural worlds, and some extra for the ships from other parts of the empire. Not only the landing strips, but also the facilities for loading/unloading goods and people and distributing them.

  • mass transit systems to connect everything to everything in a timely manner.

  • energy generators and radiators.

Additionally, the rich being the rich, you can count that in a place like Trantor they will covet empty, unused space a a symbol of luxury. Also, IIRC, there was a mountain range that was not build up (although it would have made little difference).

So, you have lots of structures that your typical small town will not include inside its calculated area, which should help lower considerably the population density.

Still, I agree that all of those are not enough to get the numbers to match; Foundation was written in 1950 where only buildings in the middle of cities where high enough to have elevators (elsewhere else it was cheaper to build lower buildings and avoid adding elevators) and these kinds of details do not age well.

  • Indeed, I didn't consider non-linear effects of so many people. Also, there may be a great deal of automation (robots) taking up space.
    – exupero
    Mar 28, 2016 at 0:44
  • I always got the impression that places like the University were rather large open areas under the dome... And other areas would be more densely populated in proportion to those open spaces
    – HorusKol
    Mar 28, 2016 at 0:48
  • 4
    @exupero If I remember correctly, the Empire did not have robots.
    – Liesmith
    Mar 29, 2016 at 2:47
  • It does mention open spaces inside the Trantor quite frequently, like the parks around the University and the park where Seldon gets attacked on his first week visiting there as a young man.
    – Franchesca
    Apr 13, 2016 at 20:03
  • 1
    @Liesmith Well, none that they knew of, and not enough to matter anyway.
    – StephenS
    Dec 11, 2021 at 18:00

The population of Manhattan in 1950 was 1.9 million, across 22.82 square miles. That's over 80,000 people per square mile. Trantor's surface of 75 million square miles being filled at 80,000 people per square mile would be a population of 6 trillion. The urban sprawl should be more dense than Manhattan per square mile due to the numerous levels of the city. So 6 trillion is a low estimate.

The city imports all its goods, and is dedicated to managing the empire, so there wouldn't be any large areas dedicated to farming or manufacture. The city is geothermal powered, but I doubt power generation would take up much space. Even if it took an entire level, there's still many more levels to have living quarters. The near entirety of the city would be houses, goods and services, tourism, and office space.

If you've been to a city, you'd have seen that thousands of people per square mile isn't all that dense. There's plenty of space nearly everywhere you go, and there's plenty of areas devoid of people. The purpose of the built environment of cities is to house and serve the dense population. So Trantor having people spread out so far, with multiple levels, doesn't make sense. 40 billion wouldn't be enough for all the retail salesmen for all the stores across the planet.

So why did Asimov choose 40 billion and not 39 billion? Or 42 billion? I can't read his mind, but I can assume that he just wanted a big number that didn't seem too ridiculous. So he just chose a nice even number that was some order of magnitude larger than the known Earth's population at the time (2.5 billion), and didn't bother doing the necessary calculations for a minor detail in his book.

  • 3
    This is the correct answer. The Foundation series doesn't have very serious worldbuilding or logistics. There's no reason to expect the Trantor population number to make any sense when virtually nothing about the economic or political situation overall makes any sense. The galactic empire serves as a convenient backdrop for a series of just-so stories, historical allusions and in-jokes, and re-purposed Encyclopedia Brown tier mystery story tropes. They're great stories and immensely entertaining, but the worldbuilding is not rigorous.
    – tbrookside
    Nov 28, 2022 at 13:10

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