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Picture, in a near future, that we build cities vertically rather than horizontally. Need a new city block? Add another few floors. Disregard for the moment any physical construction problems this may present.

My question pertains to the reason(s) for building such a city. Why would we do it? It was suggested on this question that the reason could be expanding population, but I would also like to see what other people might be able to suggest.

Note: It is important that you don't think of this as a city of skyscrapers. Everything is in the towers. As I used for an example above, city blocks would literally be a few more levels. Regular urban houses would be just another part of the massive towers.

EDIT: I have marked Vincent's reply as the answer. However, for anyone else who might have this question, I also found Peteris' answer and Joe Bloggs' answer to be very helpful.

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    $\begingroup$ This often occurs naturally as a combination between overpopulation and immovable borders... A google search for "densest cities in the world" turn up several small island cities, plus a fascinating history of Kowloon Walled City. $\endgroup$ – Lindsey D Sep 10 '15 at 17:07
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    $\begingroup$ Why build it? Because most land is flooded with rising sea water? $\endgroup$ – Hannover Fist Sep 10 '15 at 19:06
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    $\begingroup$ Doesn't Japan already do this? They've got limited land, being a mountainous island, and a whole lotta people. $\endgroup$ – Roddy of the Frozen Peas Sep 10 '15 at 19:10
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    $\begingroup$ so, you mean like an arcology? $\endgroup$ – LindaJeanne Sep 10 '15 at 21:21

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We are already doing it, all around the world.

  • Lack of space: Population and lack of available space drive the price of the land to very high levels. Other things like speculation also increase the prices but it's not usually a long lasting trend.

    People want to live near the center of the city, not 100km away. The demand is very high but the land is limited. Well, maybe the pressure would be smaller if commuting took less time. Having better transit systems will lead to the creation of an urban sprawl. Then, we have another problem.

  • Lack of space 2: It's not a good thing to cover the whole planet of bungalows. We need to grow food, we need parks and natural forests. Put it simply, we need to have a natural environment and not just concrete. Many cities have laws against building in some areas for environmental reasons (preserving the wetlands) or sometimes for historical reasons. Some rural areas are protected because they are part of our patrimony.

    Therefore, although it's not always effective because of corruption, we have an incentive to limit the growth of our cities. Cities continues to grow because the world population is still increasing and because the urbanization is not finished. In developed countries, people are leaving the rural regions to live in the cities (That is the case in Canada at least).

    So these laws are limiting the available space to build, increasing the need to expand the cities vertically instead of horizontally.

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    $\begingroup$ I like this answer. I would also possibly add an idea that I think is being missed. Enemies/Predators. People may build upwards because it's easier to fortify a smaller area than it is to secure an open city. $\endgroup$ – zfrisch Sep 10 '15 at 17:16
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    $\begingroup$ I think the farm/natural areas is likely the most compelling - farmland doesn't stack well, but we do. $\endgroup$ – Allen Gould Sep 10 '15 at 18:00
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    $\begingroup$ @AllenGould Disregarding any vallid comments until I collect my thoughts, let me say I love your last line. "farmland doesn't stack well, but we do." Sounds awesome. $\endgroup$ – Thomas Myron Sep 10 '15 at 23:01
  • $\begingroup$ @TommyMyron We could do vertical farming but right now, it can't solve our problems. At best it would reduce the pressure but we still need open spaces. $\endgroup$ – Vincent Sep 10 '15 at 23:59
  • $\begingroup$ @AllenGould there is plenty of research into vertical farming as well as somewhat more significant industrial farming in buildings, with artificial lighting. This is far more water and space efficient and in areas where energy is relatively cheap but water/space limited it can be quite effective. $\endgroup$ – enderland Sep 11 '15 at 0:05
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Why don't we do it ?

An useful way to explore why and how we might start doing something is to look at the reasons why we aren't doing it (or not doing it as much) right now.

Why don't we routinely expand existing blocks upwards if we want more apartments or office space?

Nonextensible buildings

Current buildings are generally built to be (almost) as tall as their infrastructure will allow. Sometimes they get extended to add some extra space above, but only to a very limited amount - simply adding a bunch of extra floors will risk a structural collapse, so it's not done and also prohibited by construction regulating authorities. If people want a taller building, current practice involves demolishing the current building and starting again from the foundations.

If you implement a technology that allows to extend existing buildings without extending the load-bearing structures, then it might be an entirely different result, and the places which are currently very dense and with extreme real estate costs (e.g. Manhattan) may quickly become something like your proposed tower cities just because they suddenly can. The real estate owners are limited by available land and by existing investments - with sky-high real estate prices you still won't rip down a 100 story building just to make a 105 story building; but if you had the ability, then just building the 5 extra stories would happen whenever demand justified the construction costs.

3D Real estate rights

Currently, there is no legal way to build something on top of another building without the consent of whoever owns the building below. All land plots generally have a specific owner, who then control the construction in a 2D plot of land, and everything above it. This means that if I want to "join" a city, my only options are to either to move in with people already there or to build a new house next to it horizontally. On the other hand, if real estate legislation suddenly managed 3D plots of space, then it would suddenly have lots of free available 'plots of land' for housing near the desired locations. Sure, it requires lots of tech, but with widespread flying cars, a location with 5 minute vertical commute would be much more desireable than a 50 minute horizontal commute.

Tech would allow existing real estate owners to capitalize on their monopoly on a desireable spot even more; but 3d real estate rights could enable a massive resettlement to currently empty space, if they are distributed in a way that actually enables most people to build their houses there.

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  • $\begingroup$ Non-extendable buildings - What if we took the existing buildings in four city blocks that are adjacent to each other (e.g. form a square) and connected them with metal supports? It would merge the three towers into one, with a base the square size of one of the previous four. Would such connected bases be stable enough to support more levels? $\endgroup$ – Thomas Myron Sep 11 '15 at 3:52
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    $\begingroup$ @TommyMyron It would help with lateral stability but it will not help the load bearing structures - the first floor walls or structural pillars (where the building has a load bearing 'frame', not load bearing walls, not sure what's the proper english engineering term) have to carry an enormous weight; they're engineered with a significant reserve, but it's still limited. A major change would require either a big, boring improvement in materials - something light, cheap and sturdy to replace steel and concrete for the load bearing parts; or some major fiction that enables "flying buildings". $\endgroup$ – Peteris Sep 11 '15 at 13:34
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Building up when you still have the capability to build outwards is resource intensive and wasteful. Not only do you have to consider the initial outlay, but you also have to manage resource movement and logistics for the entire tower. This is a nontrivial problem. Just look at the Burj Khalifa's plumbing and work out how much effort it takes to pump water that high.

If we're discounting high population density as a reason for doing this the only thing I can think of is to show off. Building a high city with amazing views and keeping swathes of unspoilt countryside around is a pretty powerful status symbol for the country that can do it, but it's fundamentally flawed in an economic sense.

Just for fun though: lets look at some potential reasons and why they aren't actually that good as justifications:

Spaceport access: Taller city = higher spaceport = easier to get to space, right? Nope. Not only do you still have to get the components/people/fuel up the skyscraper city in the first place, the height difference is only going to go a tiny way towards the energy needs for getting to space and, more importantly, getting up to orbital velocities

Reducing commute times: More compact city = shorter commute as you don't have to go as far, right? Nope. The elevator requirements for skyscrapers can be complex and might lead to people having to cross a whole floor to get to an elevator to take them up to the floor they need to be on to cross back across the floor to get to work.. phew

Efficiency: A'la Asimov's Caves of Steel series, it might seem to make sense to condense everything so you can process everything centrally and in the same way. Again: this doesn't work in reality, as the logistical concerns begin to outweigh any potential gains very quickly

Moving cities: This seems reasonable at first. Despite the fact that it essentially comes back to a question of high population density, it seems to make sense to put lots of floors on your moving city, however: If the city is ground based you have to worry about the centre of gravity and wind concerns, so it makes more sense to make a dome shaped or zigguratesque city (Similar to Mortal Engines). If you have an airborne city you want to spread the load as much as possible to get as many engines/zeppelins as you can, so a flatter city works better there. If you're in the ocean a decent depth of keel could improve the cities stability, but only if it's also strong enough to take the increased pressure on the lower levels and also the stresses involved in dealing with waves (I think this was a plot point about a floating hotel in a Dirk Pitt novel, but I can't remember which..). Finally: Spaceborne cities would be best off as spheres, even if you're accelerating the whole thing it's the best shape to reduce the various stresses while flying and also turning

Population control: Keep the populace close and in one building and you can lock them down. You also lock yourself in with them, and if a crazy cult decides to set fire to the lower floors you're utterly boned.

Essentially: The only reason to build an upward city that makes sense is if your population density is going up. This might be because of an increase in population, restrictions on where people can build, large draw for people to be near the city centre or reduction in available city size. Or if you want to brag to all the pretty girls about how big your municipality is.

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    $\begingroup$ Re: efficiency, uh, no. Resource usage per capita, across the board, goes down as population density goes up. Economies of scale. Diminishing marginal returns may eventually conflict with the increasing logistical costs, it’s true; there may eventually be an upper limit. But I have not seen any suggestion that we are at, or even anywhere near, such a limit. Your claim of “very quickly” contradicts my research into the topic, and desperately needs citation. $\endgroup$ – KRyan Sep 10 '15 at 19:24
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    $\begingroup$ I agree with KRyan. You are trying to extrapolate from a single building(s) much larger than usual to increasing the typical size of buildings. While that may seem reasonable, it won't actually work. From logistical, and to some extent even engineering, viewpoint these are entirely different problems. $\endgroup$ – Ville Niemi Sep 11 '15 at 10:44
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    $\begingroup$ Elevarors are more energy efficient than horizontal movement. Elevators are also getting easier to build for skyscrapers now that the friction problem of carbon fibre have been solved 1km high elevator wells now possible. $\endgroup$ – joojaa Sep 11 '15 at 14:57
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    $\begingroup$ @Kryan: Efficiency does increase with population density, but at the limit of 'everyone is in one building that goes up instead of out' you've introduced a natural bottlecap on the amount of resources you can easily get into the city in the first place. If you can feed N floors with the amount of food you can move into the building, then you add another N floors, you can't get enough food into the building to feed everyone no matter how high your efficiency is. That was the point I was trying to make. $\endgroup$ – Joe Bloggs Sep 14 '15 at 8:47
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    $\begingroup$ @joojaa / Yakk: The issue with the elevators is that for every elevator well you add you're removing valuable real estate. The same is true of streets and corridors to an extent. The difference between elevators and streets is that while many people can crowd continuously along a street elevators can only deliver in discrete packets and then have to return, which makes for a logistical nightmare. The 'traffic' in this situation would be far worse than your usual gridlock. Unless we introduced a nice PRT system with some vertical rails involved, but that's a major engineering challenge. $\endgroup$ – Joe Bloggs Sep 14 '15 at 8:51
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Thinking of sci-fi, one could build vertical cities to make them fit in a spacecraft. A reason can be aerodynamism. Another reason can be to reproduce some gravity (to turn over one axe at appropriate speed).

By extension, the reason could be the will to move the building.

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  • $\begingroup$ Welcome to the site Kii, interesting perspective, I like the answer. $\endgroup$ – James Sep 10 '15 at 15:02
  • $\begingroup$ Thanks for your Welcome James ! Could you edit your comment to update my nickname please ? $\endgroup$ – Kii Sep 14 '15 at 8:19
  • $\begingroup$ Kii, comments are only editable for about 5 minutes after they are posted...so...nope! $\endgroup$ – James Sep 14 '15 at 14:30
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Build up to save the planet. Wherever humans go, they tend to spread out and consume the surrounding landscape with severe impacts on the local flora and fauna. Instead of requiring reduced impact from farming or logging, a society may choose to compress the population into the urban centers while vacating rural and suburban communities to let nature recuperate.

Moving the rural and suburban populations into urban areas requires roughly double the living space as cities presently offer. If the land area used by present urban areas is capped and no expansion is possible then the only way to house more people is to go up (or down but the OP didn't ask about building into the earth).

Cloak each new tower in hanging gardens and solar panels to reduce food and energy consumption from outside the tower.

Building that much housing, office, food growth and manufacturing space is a monumental undertaking that will take decades to achieve.

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    $\begingroup$ Limit human footprint to a relatively small area then you can turn the rest of the world into a nature preserve. Plus with "everyone" in one building you don't need roads that wildlife will get killed crossing. $\endgroup$ – Arluin Sep 11 '15 at 3:02
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To reduce CO2 emissions. It is already recommended to build high-density, mixed-use buildings that can decrease transportation needs and allow for big integrated heating-cooling systems. These benefits of medium-height, high-density don't go away when building even taller and denser if horizontal travel between the towers becomes possible.

Many technologies with the purpose of reducing CO2 emissions have impact on the ideal shape of our cities and a green future could probably go both horizontal or vertical. If immobile expensive solutions such as deep water source cooling catches on, it would draw cities in the vertical direction.

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In the near dystopian future: Fossil fuels have become scarce, this sharply increases transportation costs. Coupled with diminishing global wages and harsher climates, people around the world give up the dream of owning land - much of which has become dry and barren - and begin to concentrate in large, sturdy towers near fresh water sources where goods and services are more easily accessible.

In the near utopian future: Entrepreneurial visionaries devise low-cost, eco-friendly pre-fabbed skyscrapers that look beautiful and offer luxurious views to those who could not afford them before. Wholly self-contained, expandable "town-in-a-box" towers begin popping up in smaller cities and even rural areas, offering a trendy new low-maintenance lifestyle to a generation disenchanted with the burden of home ownership. Empty streets and vacant lots are converted to farm or green energy production, parks, bike paths or simply returned to the wild.

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One thing the other answers miss is: pride.

Building large, tall skyscrapers is very much about bragging. The pyramids weren't built for practical purposes. They were built as status symbols...as are most of the worlds 'tallest' buildings.

Tall buildings are used as personal symbols (Rockefeller center), business symbols (Transamerica Building--later a symbol used by the city), and City symbols (1 World Trade Center).

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    $\begingroup$ Pretty sure pride is the second paragraph I wrote. Or at least showing off, which is almost the same, right? $\endgroup$ – Joe Bloggs Sep 10 '15 at 16:07
  • $\begingroup$ @JoeBloggs indeed you did! I didn't post fast enough. $\endgroup$ – DA. Sep 10 '15 at 16:16
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Because It's Cheap

Since we're disregarding the physical construction issues...

Land is expensive. Land in cities can be exponentially more expensive. Think about the million-dollar-a-year New York apartments you hear about. Cities have to pay and manage land as well as individuals, so a small city would be incentivized to build up instead of outwards since this is usually done by area.

Now obviously there's an economic relationship here - if you can build higher, land becomes less valuable. But certainly you would see higher construction than we currently make, at least until the point where the cost of going even higher balances out the value of the location.

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Looking into Paolo Soleri's works on arcologies might be of interest to you. He conceived of the idea of a self-contained city-in-a-building in the 1970's or thereabout. His idea was to provide a small-footprint city in places that might be otherwise unusable or uninhabitable.

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The most important reason would be to shorten distances. In a tall city you can fit a lot more room within walking distance.

@JonBloggs lists a lot of excellent reasons not to do this, one of which is that elevator systems for tall buildings are complex and difficult.

This is the result of everybody having to go to ground level to get anywhere. If you build exits and transportation paths at multiple heights this will be improved. In addition to the street net, you will have connections at, say, every 25 stories. Both pedestrian and motorized. With ramps leading up and down too. Finding the right bus to where you want to go would need computer assistance.

People living low down will not get much sunlight and this will NOT be popular. Expect resentment. If you have cheap power, you can set up fake sunlamps.

Fire will be a serious problem. No wood allowed. Paper severely restricted. Plastics? Call the cops!

We are already building tall. In the most crowded cities, buildings are as tall as we can make them (or could, when they were new) This is not going to end.

[Edit add]

Oh, I almost forgot: Aqueducts! Put the water supply at the level of the tallest buildings, makes plumbing so much easier.

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Since you tagged it with "near-future" this might not be a good answer but if you were willing to consider the distant future... For some reason, you might want to move an entire city... (e.g. a proliferation of natural disasters, constantly moving war-zones / fronts / borders, the population collectively wants a holiday in the sun, etc.)

A lot more practical if the entire city is contained in one building (and you have the technology to move a very large building)

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  • $\begingroup$ Practical? Yes. Works with the story? Unfortunately, no. I need multiple towers. $\endgroup$ – Thomas Myron Sep 11 '15 at 14:27
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There are already a lot of good answers here so I hope my small addition will be valuable.

There are a few pre-planned & designed cities engineered for advancement in technology and often decreased environmental impact.

Masdar City is the one that, to the best of my understanding, comes closest to the concept I want to present, (skip down to the Architecture section & skim a bit).

To add to the Masdar City link I would like to direct your attention to the design of termite mounds. I think it's valuable to consider both the real design value of termite mounds as well as the generally accepted & long standing belief of their value (as both could be accomplished with a large and possibly segmented tower design).

Concept:
The basic concept is to make a city that is self sustaining.
The value of my referenced material is that it has been proven in Masdar City & the Zimbabwae sky scraper that it is possible, through correct design, to passively control the environmental temperatures of a coherently designed structure.
In addition the more correct understanding of the design of a termite mound proves that ventalation & moisture control can also be accomplished passively.

The requirement of all of the above is, effectively, a single integrated structure, therefore supporting the design choice of a single tower like structure.

Let me add one additonal thought, the value of this might be increased in hot arid lands/planets.
(though I haven't put much thought to it, there's a chance this might be true of cold environments/planets as well... )

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