How realistic would a city of over ten million people in an area of less than 100 square kilometres be?

Question

I have been playing Cyberpunk 2077 on my PS4 and Night City in the game has almost 7 million people and an area of just 75 km². It is very dense with suspended streets and highways and giant buildings that house a million people - functioning as a city inside a building. It has many homeless people as well.
Of course I know that the PS4 probably does not have enough processing power to render such an immense population in a small area so I am curious if the same could work in real life.

Environmental needs and regulations could make big cities become more and more dense and compact over time, but how could such a city work, and how would people live in it?
Take Manhattan for example: it has less than 100 km² (it is around 60 km²), but it has around 1,5 million people living in it. I have never been there, but from pics and videos it looks very dense and it has very tall skyscrapers. Imagine if the entire New York city area (that's over 8 million people in an area of around 800 km²) had the same size as Manhattan, which is even smaller than the Night City area of Cyberpunk.
Or what about São Paulo (which has an area of around 1500 km²), which already has over 12 million people in an area of less than 100 km²?

Answer 1

A cyberpunk setting tends to be both high-tech and dystopian.

We are talking about 10 square meters ground footprint per inhabitant. Assume that half of that are roads, rails, footpaths, and the few remaining parks. Assume that half of the remaining area are commercial buildings. That leaves 2.5 square meters per inhabitant.

That sounds unrealistic, even for the worst favela. Say that the average building has 20 floors, and you get 50 square meters. A high-rise will spend some area on stairwells, lifts, corridors, and utilities. Pulling a number out of thin air, 50%. That means 25 square meters, 270 square feet, per inhabitant.

That sounds crowded but do-able for a single-person flat, and almost reasonable for a four-person household with 100 square meters. No second bathroom, but hey, could even be individual rooms for the kids. And keep in mind that those are averages.

• Put one or two million into coffin hotels, and redistribute the balance of their slice to the upper classes.
• Despite of my comments above, put one or two million into very crowded favelas. They might live in single-story dwellings, but two or three to the 5 square meter shack.
• Put six million into roughly average Plattenbauten. Working 8-to-6, commute on top, all to pay the rent and marginally healthy food.
• And then there are the upper classes, either in larger apartments in better high-rises, or even in genuine mansions and penthouses.

But you would need a very good reason to stack people that densely, instead of sprawling into the suburbs.

Answer 2

The only real problem with a city of the proposed size is logistics. It is not hard to build enough dwellings for the population -- just go vertical and you can have comfortable and sufficiently big living spaces.

For comparison, in the 700-800s Chang'an had a land area of about 90 km² and a population of approximately 1 mln people. Most buildings were single-storey ones. The city also included large forbidden grounds where the imperial palace and the courts were located.

If you build 20-30 storey buildings¹ you should be able to house people and have enough room for shops, offices, etc. Whether there will be homeless people or not depends on political and cultural factors more than anything else. All developed countries in our world have enough land and resources to provide homes for every single one of their citizens, but not many choose to do that. Finland, and specifically Helsinki, is an example of how it can be done.

The most obvious logistical problems are:

• food

  People need to eat and it is challenging to produce enough food for all city dwellers inside the city. While some food can be grown/manufactured within the city (vertical farming, algae farms, artificial meat are just some of the possible approaches), it is very likely that most of the food will have to be delivered from elsewhere.

  Delivering food into the city is not enough, though. It should be distributed as well. It might be a good idea to have shops either in every building or one for a certain number of buildings. This would make distribution more efficient and optimise commute.

• waste

  Cities produce a lot of waste. It might be a good idea to process at least some of it on-site. For example, in Tokyo, some buildings have furnaces for burnable waste. The energy can be used for heating water.

  Recycling and at home rubbish sorting should be the norm.

  It would also help if packaging was reduced. There is no need to have 2-3 plastic wrappers for one small tiny thing. Perhaps, packaging can be made of easily degradable, compostable materials, that are collected and used as a fertiliser.

• sanitation

  This relates to water, sewage, and human excreta. Water should be clean and readily available (lack of clean drinking water may lead to the spread of diseases). I think sewage and human excreta are self-explanatory. I am not sure what are good solutions for these problems. Please do your own research.

• commute

  The best solution for commuting is public transportation. It is cheaper, safer, and allows for a greater number of commuters. There are plenty of options for this: buses, trolleys, underground, trams, trains, suspension railways, etc. The most important thing is to have a stop for at least one type of transportation within a short walking distance from the starting and destination points. I think that a 10-min walk would be great.

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¹ If this is still not enough, build higher buildings or dig deeper. A Cyberpunk universe should have the technology for this kind of construction projects.

Answer 3

Short answer.

The population density of Night City can be attained and has been exceeded in smaller communities.

Long Answer in Four Parts.

Part One: How to achieve high population density in relative comfort for the population.

The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong (66 by 660 feet), which is exactly equal to 10 square chains, 1⁄640 of a square mile, 4,840 square yards, or 43,560 square feet, and approximately 4,047 m2, or about 40% of a hectare. Based upon the International yard and pound agreement of 1959, an acre may be declared as exactly 4,046.8564224 square metres. The acre was sometimes abbreviated ac,1 but was often spelled out as the word "acre".2

https://en.wikipedia.org/wiki/Acre

So an acre is about 208.71032 feet by 208.71032 feet, or about 63.616 meters by 63.616 meters.

I think that the lot where my family lived for some years was about half an acre in size, which would have been about 208.71032 feet by 104.35516 feet, or about 63.616 meters by 31.808 meters.

I believe that the house there was about 30 feet wide by about 40 feet long, and thus with about 1,200 square feet (111.48 square meters) per story or floor. It had three floors and a basement, so it had a total of about 4,800 feet on four levels. Assuming that each level was about 10 to 14 feet (3.048 to 4.26 meters) tall, the house was about 40 to 56 feet (12.19 to 17.06 meters) tall from the basement floor to the roof.

Imagine a building with such lots and houses stacked one above the other. Each lot could have girders (perhaps disquised as trees) about 40 to 56 feet (12.19 to 17.06 meters) tall spaced around spaced around the perimiter to hold of the ceiling and the floor above. And each building could have girders about 40 to 56 feet (12.19 to 17.06 meters) tall supporting its walls and floors and supporting the girders in the next level above it that support the next house above it.

So if that building containing those lots and houses was 40 levels high, 1,600 to 2,240 feet (487.68 to 682.75 meters) tall, and was one mile square (2.58998811 square kilometers), it would have room for 1,280 house and lots on each floor, so it would have room for a total of 51,200 houses and lots. With about 2 to 10 people living in an average house, there would be 102,400 to 512,000 persons per square mile or 39,536.8 to 197,684.3 persons per square kilometer.

Now imagine that the lots contain one story houses. The medium size of single family homes in the USA is about 1,600 or 1,650 square feet (148.645 or 153.29 square meters), considered to be the largest in the world. A single story house of such square footage could be 40 to 40.62 feet (12.19 to 12.38 meters) on each side if square, 28.28 by 56.568 feet (8.619 by 17.24 meters) to 28.72 by 57.44 feet (8.75 by 17.5 meters) if twice as long as wide, etc.

Such as house could easily fit in a half acre lot (about 208.71032 feet by 104.35516 feet, or about 63.616 meters by 31.808 meters) or a quarter acre lot (about 104.35516 feet by 104.35516 feet, or about 31.808 meters by 31.808 meters).

If a building contained 100 levels of single floor houses on quarter acre lots one above the other, and was a mile square, it could contain 2,560 houses and lots per level, and thus a total of 256,000 houses. So with two to ten people living in the average house, it could have 512,000 to 2,560,000 persons per square mile (197,684.3 to 988,421.5 per square kilometer) of ground it occupied. With 15 to 20 feet (4.57 to 6.09 meters) per level the building would be 1,500 to 2,000 feet (457.2 to 609.6 meters) tall.

Naturally there woould have to be streets between lots for pedestrians, bikes, electric cars, trucks, emergency vehicles, etc. And presumably each floor would have shopping centers and other public buldings, so that people wouldn't have to travel up or down too many floors for routine activities. So the actual number of people living in the building might be only a half or a quarter of what it would be if the building only contained houses and lots.

So such buildings might contain only 25,600 to 1,280,000 persons per square mile of ground space they occupied (9,884.2 to 494,210.75 persons per square kilometer).

Each person might have 202.342 to 4,046.862 square meters of space in the building.

There are various other problems with such vertical city-in-a-bulding concepts, but if they are solved people could live like small town or suburban Americans in buildings with high population densities.

...and Night City in the game has almost 7 million people and an area of just 75 km2.

That gives a population density of 93,333.333 persons per square kilometer. Which seems to be about the midpoint in the range (9,884.2 to 494,210.75 persons per square kilometer) of the population density of my hypothetical giant buildings designed to enable the inhabitants to live similar to suburban or small town Americans. And of course it is not a requirement that the people in Night City live lives that good. They can live in much more crowded squallor.

Part two: Night City vs real cities.

...and Night City in the game has almost 7 million people and an area of just 75 km2.

That gives a population density of 93,333.333 persons per square kilometer.

At the present time the major city with the highest density is Manila, the Philippines, with 41,515 persons per square kilometer, 0.4448 the density of Night City. And probably only a minority of the people in Manila live in 40 to 100 level high rise buildings.

https://en.wikipedia.org/wiki/List_of_cities_proper_by_population_density

Part Three: Night City vs real city districts.

There are eight city districts around the world with populations between 101,693 per square kilometer and 177,038 per square kilometer, significantly higher than Night City.

https://en.wikipedia.org/wiki/List_of_city_districts_by_population_density

So an entire city that had the same population density as those districts would have a higher population density than Night city.

Part Four: Night City vs the Kowloon Walled City.

The legendary Kowloon Walled City in Hong Kong was a small area which achieved a very high population density in multistory apartment buildings.

By 1990, the walled city contained 50,000 residents1 within its 2.6-hectare (6.4-acre) borders.

https://en.wikipedia.org/wiki/Kowloon_Walled_City

the city also underwent massive construction during the 1960s, with developers building new modular structures above older ones. The city became extremely densely populated and "a world unto its own," an enclave,[14] with over 33,000 people in 300 buildings occupying little more than 7 acres (2.8 ha).

https://en.wikipedia.org/wiki/Kowloon_Walled_City#Urban_settlement

The first statement gives a populartion density of 1,923,076.9 per sqaure kilometer, the second gives a population density of 1,178,571.4 per square kilometer.

A thorough government survey in 1987 gave a clearer picture: an estimated 33,000 people resided within the walled city. Based on this survey, the walled city had a population density of approximately 1,255,000 inhabitants per square kilometre (3,250,000/sq mi) in 1987,[20] making it the most densely populated spot in the world.[55]

So the small area of the Kowloon Walled City had a population density 13.446 times that of Night City. If an entire city of 7,000,000 people could achieve the population density of the Kowloon Walled City, it would need an area of only about 5.577 square kilometers.

https://en.wikipedia.org/wiki/Kowloon_Walled_City#Demography

. As a result, the city reached its maximum size by the late 1970s and early 1980s; a height restriction of 13 to 14 storeys had been imposed on the city due to the flight path of planes heading toward Kai Tak Airport.[15]

https://en.wikipedia.org/wiki/Kowloon_Walled_City#Urban_settlement

The walled city was located in what became known as the Kowloon City area of Kowloon. In spite of its transformation from a fort into an urban enclave, the walled city retained the same basic layout. The original fort was built on a slope[44] and consisted of a 2.6-hectare (6.4-acre) plot measuring about 210 by 120 metres (690 by 390 ft).

https://en.wikipedia.org/wiki/Kowloon_Walled_City#Layout_and_architecture

Ignoring the narrow allys and courtyards, one can think of the Kowloon Walled city as a single building covering about 210 by 120 meters and 13 or 14 stories tall.

So the total floor space would be about 327,600 to 352,800 square meters.

That would give a total of about 6.552 to 10.69 square meters per inhabitant.

Conclusion: It is possible for a community to reach and exceed the population density of Night City. How desirable or not that would be would depend on the design of the city.

Answer 4

Pressure:

As has been pointed out several times here, the physical logistics of cramming more and more people into a small area have already been done around the world, and with cyberpunk tech, that just gets easier.

The real challenge is explaining WHY so many people want to live in such a small area. What is the force pushing everyone into a tiny area?

• Environmental: The world is full of toxic (air?), or lethal solar flares, and outside of a few regions, no one can live for long. Technology allows super-dense hydroponics and aquaculture, supplying food for everyone retreating to the limited zones as the world collapsed. Now millions live in mega-cities because they CAN'T live anywhere else. The cities are hermetically sealed and shielded from the outside.
• Eco-supremacy: Environmental radicals have decreed that sprawl is evil and humans must live in hyper-dense conditions to minimize their impact on the environment. While the sights of former cities return to nature, people must live packed in like sardines eating yeast and vat-grown algae.
• External: The aliens showed up and forced mankind off the land, which they now use for (environmental remediation/drug growing/alien recreational areas). The Earth is now colonized, and we live at the mercy of our alien masters.
• Defense: The zombies/diseased/techno-nomads are really bad out there, and no one outside the walls lives for long. Man has fled to fortresses to protect themselves, and only the easiest defended spots are suitable for people to live. The rich need endless cheap soldiers to protect their interests.
• Resources: A massive asteroid made of pure iridium or an alien artifact that can manipulate physics sits in Antarctica. It sparked a massive gold-rush of development, in a world of crushing poverty. There is a huge demand for labor to work the (mines/factories) associated with it, but conditions are harsh and the people running the area have constructed a massive arcology to supply the workers with what they need.
• Runaway wealth gap: The rich all live in palatial estates around the world, and own all the means of production. Human labor is irrelevant as machines do all the productive tasks. "Normal" people are a nuisance, and the rich have decided to isolate them to smaller and smaller areas as they claim more and more land for their own causes. The government doesn't allow the poor to be exterminated, but they are driven into hyper-dense enclaves where they have steadily less food, less water, and cheaper and cheaper drugs and entertainments. Most people live in a virtual escapist reality while lying all day in pods hooked up to life support.