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Question: I'm trying to determine how large (geographically) my city will have to be to accommodate for 1 million people.

I have a city that was basically formed by the gods to be fertile land with a good climate for crops (there are all four seasons) and to look like this:

Circular city with mountains to the north and a river running around it

That's not exactly how the river runs around the city, but the basic idea is that the land spirals from the place where the river enters the city down to where it exits.

The city is split by the river into 8 octants, each octant is almost completely identical to the others. In the middle is a huge palace where 8 rulers live, surrounding the palace is the octant "administration building" then immediately out from that is where other normal city buildings are (textile shops, hospitals, etc.).

From there you get to people's dwellings. The dwellings can definitely be multi-story apartment-like buildings. They're very effective at building tall/strong glass buildings (their magic system helps with that and the tall palace is evidence of this). The dwellings are arranged so that the people who work in the center of the city first, then people who work further out second. Then you get to the second layer of normal city buildings (so there's an inner hospital and an outer hospital for each octant). Finally you get to a third set of dwellings for the people who work out in the fields (farm and livestock land) and forests which surround the city.

Here are some useful bits of context:

  • This is a world for a fantasy novel where the gods shaped the land to be suitable for this.
  • The civilization is sitting somewhere around the 1800s in our own history as far as technological capabilities.
  • This city is optimized for efficiency, not citizen's enjoyment. So sports and things like that don't have a place here and therefore wont take up space.
  • They use the river to travel and transport goods throughout the city (as I mentioned, the drawing is imperfect because it doesn't really communicate how this works very well).
  • They build most things out of glass (they get the sand from huge sand dunes in the east), but they do use metal (mines in the north) and wood for some things. The trees are within the boundary of the river.
  • The city is completely self-sustaining. With the exception of mines that are out in the mountains to the north and sand dunes to the east (the entire city is built out of especially strong glass to enable the sun-powered magic), everything the people need to survive and thrive exists within the boundary of the river.
  • The people in the city also completely share resources. Everything comes to the administration buildings and is equally distributed. No "class" system. This means that everyone's homes will be the same size relative to the size of their families.

So what I need to determine is what the diameter of the city would need to be to accommodate ~1 million people. How big would the fields need to be in relation to the dwellings etc. I need to know this so I can accurately describe how long it would take someone to travel from the palace to the outside of the city given various modes of transportation (walking, riding in a carriage, and riding on a barge on the river).

Thanks!

kentcdodds
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  • Hello and Welcome to worldbuilding. Boy have you chosen a complicated question to ask.... I'm not sure if we could answer it without a book. We've had a couple of these self-sufficient city questions asked before and they are usually closed because it is far too broad of a subject. Just a few clarifying questions? What technology level is this city? And does this sun powered magic contribute to society or can we ignore it? – Shadowzee Feb 11 '19 at 05:23
  • Updated to indicate technological level of about 1800s in our history. The sun powered magic could potentially help, but can mostly be ignored for this question I think. – kentcdodds Feb 11 '19 at 05:25
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    At about 1800, the energy roughly divides out to about 20% human muscle, 20% animal muscle, and about 60% wood. This might help you work out some of the area relationships, though I'm not sure precisely how. The other problem you have is that you've not specified the environment. This could be anywhere -- the poles, the equator, or most anywhere. Production and the land required for it varies widely, I think, depending on many different factors. It may help get better answers if you add something about the climate and land type. – jonk Feb 11 '19 at 05:37
  • Thanks! Will add that context! – kentcdodds Feb 11 '19 at 05:38
  • "self-sustaining" - does this mean all food is coming from within the city? – Alexander Feb 11 '19 at 08:55
  • "The city is completely self-sustaining": a self-sustaining city does not exist has never existed. I cannot even see the point of a "self-sustaining" city; the entire reason of existence of a city is that it concentrates trade and industry, explointing network effects and economies of scale; the city brings in food, raw materials and trade items for elsewhere, processes them and exports the processed goods. – AlexP Feb 11 '19 at 09:36
  • Sorry @AlexP, but this city must subsist in total isolation from everything else in the world. It's a key part of the story. Alexander, all it means is that all the needs of the people of the city come from the city itself. The inhabitants of the city are completely unaware of the existence of any other city (this is made possible by the god of the world). – kentcdodds Feb 11 '19 at 13:46
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    This is not a duplicate but a question with some overlap and an answer that can apply to your question as well. https://worldbuilding.stackexchange.com/questions/121397/largest-population-for-ancient-world-migration-encampment – Cyn Feb 11 '19 at 16:06
  • @kentcdodds then you need to explain how the food is grown. Do you have traditional farms and fields? – Alexander Feb 11 '19 at 17:28
  • If the buildings are made of glass, probably making every building a toasty little greenhouse, are they practicing indoor farming? – Adam Miller Feb 11 '19 at 19:23
  • If it's supposed to get all its food from within the walls, roughly as shown in your picture, you will not have a city, but a village with a few hundred people. (Indoor farming doesn't really help much: you can get an upper bound by computing (area exposed to sunlight) * (photosynthetic efficiency) * ~750 w/m^2 and converting to calories.) – jamesqf Feb 11 '19 at 19:52
  • Is this city based off of Tenochtitlan (the Aztec capital)? Cause it looks and sounds like a very similar design - which had a population between 200,000 & 350,000 on 13.5 sq km (5.2 sq mi). @Alexander though I agree that no city-state can exist without trade maybe they used floating gardens? (and note the use of city-state as they may have localized trading - i.e. its a mini-Europe or US cause with 1 mil population it could be a mini-nation) – LinkBerest Feb 11 '19 at 20:16
  • @Alexander, yes, as I explain that there are people who work out in the fields. But I could call that out more by using the word "farm" :) – kentcdodds Feb 11 '19 at 20:34
  • Please note that this is for a fantasy novel so whether there have ever been or will ever be self-sustaining cities in reality is irrelevant. The fact is that they do have everything they need to thrive. I don't know why trading would be so important if they have enough land to farm and subsist themselves. – kentcdodds Feb 11 '19 at 20:37
  • @JGreenwell, this is not based on anything else, but many people have mentioned there are similarities with other fictitious cities. The city was also literally constructed from a god so normal issues of land not being capable of supporting a city like this is also not a problem here. – kentcdodds Feb 11 '19 at 20:39
  • So, do we need to include "fields and forests which surround the city" into city's total area? – Alexander Feb 11 '19 at 20:40
  • Yes, that's another inaccuracy of the picture. The water surrounds the trees as well as the farmland. The only thing the people in the city travel outside the water boundary for are mining deposits in the mountains to the north and sand dunes (for their glass) in the east. – kentcdodds Feb 11 '19 at 20:42
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    the city I'm referring to is not fictitious (ancient yes but not fiction) - I would still search it because it solves (at least partial) a lot of the problems that comments are pointing out and it is very similar in design/isolation as your proposed city (it was a floating city on a lake) – LinkBerest Feb 11 '19 at 20:43
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    When it comes to pure population density, look at two real-world examples, Riyadh (Saudi Arabia) and Manila (Phillipines) - The latter has a more than tenfold population density than the former. (46.000 vs. 3.600/km²) – tofro Feb 12 '19 at 10:31
  • @tofro: But neither Riyadh nor Manila, nor any other possible city, gets any significant fraction of its food supply from within its boundaries. It is simply not possible. (Absent food-producing magic, of course.) – jamesqf Feb 12 '19 at 18:52

4 Answers4

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In the picture you provided the fields seem to be enclosed by walls and thereby probably count towards the city size.

Size with fields: 2312.32 km2

Size without fields: 312.32 km2

Why?:

Fields: For the field size I used this source; according to it, 4 people need 2 acres of land, which is about 8000 m2. This means 2000 m2 per person, times a million, gets us 2000 km2.

Rest of the city: I used London at the beginning of the 19th century (at that time it had a million in population) and encompassed 122 miles2 or 312.32 km2.

Glorfindel
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Soan
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    Given that his pictured city includes sky scrapers, his city probably has a higher population density than turn of the 19th century London. But of course, this difference is small compared to the amount of farmland. – Shufflepants Feb 11 '19 at 16:24
  • FYI, that puts it at a healthy 23 km radius. – Azor Ahai -him- Feb 11 '19 at 17:06
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    @AzorAhai Make that 27. – Mr Lister Feb 11 '19 at 18:18
  • @MrLister Oh oops I confused it with the surface area of a sphere lol – Azor Ahai -him- Feb 11 '19 at 18:42
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    I think the problem of using London as a model is that it wasn't self-sustaining. For example, it was at the time the world's largest port. – jonk Feb 11 '19 at 20:23
  • @Shufflepants, 1800s London may not have had modern skyscrapers, but it certainly had dense vertical construction, with buildings as tall as was practical prior to the invention of the elevator. – Mark Feb 11 '19 at 22:39
  • @jonk, London is still a good model for how dense the urban fabric would be. – Mark Feb 11 '19 at 22:41
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    @Soan, note that your source for farm area is assuming modern high-density farming techniques and crops. Using 1800s technology, you might manage that density in someplace like the Nile Delta or Bangladesh, but for most of the rest of the world, you'd need to at least double the area needed. – Mark Feb 11 '19 at 22:47
  • @Mark If I'm understanding your comment, I think you are just looking at the living space and shops, perhaps. But that's a small part. Then, 60% of the energy came from wood. I've looked at some cases (just a few) of self-sustained living (discounting tools and ore refinement) that places a figure of 4-5 acres per family, without access to modern supply chains and when the land is fertile and the climate moderate. (< 1/4 acre is enough, otherwise.) Animals play an important role, too. So I still don't think 1800 London is even close to a good measure, given external infrastructure it required. – jonk Feb 11 '19 at 23:11
  • @jonk, 1800s London was a net exporter of goods. No, it wasn't entirely self-contained in terms of factories and other urban-support infrastructure, but it provides a reasonable approximation of how large a self-contained city would be (not counting farms and energy sources). – Mark Feb 11 '19 at 23:17
  • @Mark I disagree on the "net exporter" result. But you'd need to provide your sources (what was exported, exactly, and how the "net exporter" is determined [was it by market value of goods, for example?]) And then I'd need to provide mine. This isn't the place for an extended discussion, anyway, and I'm sure it will be deep-sixed if we tried. So we simply will have to disagree and let the OP decide what's important to them. – jonk Feb 11 '19 at 23:25
  • @jonk That's why London was only used for a model for how much space would be given over to housing and industry (312.32 km²) - the "external infrastructure" (farms, forests, etc) would be the other number calculated (2000 km²) which then needs adding on, and is what you actually appear to be trying to disagree with instead. – Chronocidal Feb 12 '19 at 08:22
  • @Chronocidal Those details are important. Anyway, I think we'll leave the topic. An answer has been selected, already. – jonk Feb 12 '19 at 08:25
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Without consideration for comfort and open space you can look at the list and pick Manila as your model.

The highest density city in the world at 119,600 per square mile, you'd need less than 10 square miles for your city of 1million. The thing to note is that Manila isn't really high rise. It's very densely packed low and medium rise with minimal open space.

Separatrix
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  • I doubt that Manila grows any significant amount of food. – jamesqf Feb 11 '19 at 19:54
  • @jamesqf, cropland wouldn't normally be considered within city bounds – Separatrix Feb 11 '19 at 20:58
  • Normally, yes, but the OP states that everything (except metal from mines, and sand) comes from within the city boundary. Which (absent food-making magic) is utterly ridiculous. – jamesqf Feb 12 '19 at 18:47
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I found this on farmland necessary to sustain some amount of people: How many people can you feed per square-kilometer of farmland? so using conventional farming (no hydroponics, magic, or crazy stuff), you'd get around 2350 people per km2. Flip it around and that's about 425 km2 for a million people.

Ok, then I looked up population density for one of the major US cities that I'm familiar with. About 3662 people / mi2 or 1400ish people / km2. That's about 715km2 for a million! This metric isn't ideal at all since medieval london was around 100 people/km2 which is a huge difference so you'll have to play around with this number. I read that ancient Rome (city of Rome) had around 1 million inhabitants so that might be a good reference as well

So, 425 + 715 = 1140km2 which is a circle with a diameter of 38km or 24mi. That's probably a solid start to the problem. You'd probably have to also look up how many farmers you'd need per km2 to help estimate that layer.

oh and the average human walking speed is about 3.1 mph so on a clear cross-cutting road, it'd take 8 hours to make it across with no breaks or obstacles.

fabian
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antjanus
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  • Your estimate for yield per km^2 assumes fairly modern (late 20th-century), crude oil based intensive farming methods. I don't think it's appliciable here. Also, according to https://en.wikipedia.org/wiki/List_of_urban_areas_in_the_European_Union and https://en.wikipedia.org/wiki/List_of_United_States_cities_by_population, 1.400 people/km² appears to be on the lower end in regards to population density in cities of about 1 million people. If there are a lot of tall, "multi-story apartment like" buildings it might be a little low. But that depends on the specifics of the city. – nishuba Feb 12 '19 at 10:30
  • Unless you intend to farm with purely human labor, you'll need draft animals to pull plows & wagons, and you'll need to feed them, too. – jamesqf Feb 12 '19 at 19:01
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Apartments or houses? Apartments are far more efficient when it comes to regards to their footprint. In the 1800, my guess is that the average household had about 4 to 5 people. Hence, you would need 200,000 to 250,000 housing units.

Class system will greatly influence the floor space per each housing unit. My lowest class, get about 40m2 apartment, or a 400m2 plot of land for a house. My 'rich' get 2500m2 plots for their houses.

My experimentation yielded that the housing 'efficiency' is between 65% to 75%, depending on class. What this means, is that for 100 poor houses (100 x 400m2 = 40,000m2), you would need an area of 61,540m2. Thad additional area is for your roads and streets.

My previous research yielded that a loaf of bread needs 1m2 of field space. A cow and a calf need about 1ha of grazing space. A chicken would need only 4m2 of space.

I hope this helps.

Glorfindel
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Greg Wochlik
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