With the astounding pace of urbanization throughout the developing world and decline in popularity of suburbia in the developed, it is time to search for a golden middle of population size within a given area.
Is there a rough scientific population sweet spot for a city within a certain area or is it all just personal preference? If there is one it would have to be an optimal point between economic-energy efficiency and psychological well being. Sure, a million people can theoretically be crammed into a few square blocks with each block having a hyper efficient residential skyscraper. But our intuition tells us that this ant colony-esque arrangement may run into major psychological roadblocks. If restlessness and boredom often characterizes an isolated hamlet and stress characterizes a super cramped and futuristic megapolis then a search for a compromise is essential. A rapidly urbanizing society that figures out optimal population to land area ratio is then most likely to attract and retain human capital going forward as well as solve multitudes of problems facing it more effectively.
For those thinking that a city size can't be planned, even with incentives, and that a city size is determined by relatively mysterious organic migrations of people, the fact is that in the next 40 years we wont have much of a choice but to plan from the start. With 2 billion people soon to be added to world's population and countries like China adding a million people to its cities every week, having at least a population ceiling for an area will be crucial. Recent rapid formations of unmanageable mega slums throughout the developing world shows that peripheral "organic city growth" needs to be legally limited. In addition, infrastructure built has to be protected from population related strains from the start. Even well off Western cities like Austin Texas have quickly seen their populations nearly double with formerly solid road infrastructure simply failing to mathematically accommodate. Infrastructural failure may be hard to spot but being stuck in traffic for 2 hours every day in Los Angeles or Moscow is a sign that it is already happening.
China has been having relative success with accommodating breakneck urbanization via 1) rapid city construction with multiple neighborhoods built simultaneously (the current "ghost city" real estate bubble concerns notwithstanding as even so called ghost cities will be filled eventually since there isn't such thing as having too much shelter for humans) 2) having some idea of the total final capacity, urban density, and transport loads when laying infrastructure 3) having long term multi-decade regional plans encompassing clusters of new cities and linking the clusters by high speed regional transport network.
The Chinese approach with all its pitfalls has been the best given the difficult circumstances. Beijing is currently also developing and testing concept 80,000+ strong satellite green cities (where everything is 15 minute walk away) that can be scaled up as necessary if successful. State orchestrated urbanization will be the name of the game throughout large swaths of the planet as these methods are emulated and improved upon. That is why urban theorists need to start formulating an idealized population cap for areas so we don't one day find ourselves in a future we're not exactly comfortable living in.
Lets start with psychological essentials.
Space colony studies have shown that a human needs at the very least 40 sq meters (430 sq feet) to him or herself to be in a stress neutral state (in addition to olfactory, visual, thermal, air quality factors). This absolute minimum for avoiding neurosis should automatically be increased to 50 sq meters (538 sq feet) as a criteria for city housing. This would compensate for the effects of overcrowding in public spaces and provide common sense leeway since absolute space habitat standards are obviously restraining on earth.
Beyond this, come the recent scientifically proven benefits to having a city as populous as possible. Physicist Geoffrey West has shown that:
"In city after city, the indicators of urban 'metabolism,' like the number of gas stations or the total surface area of roads, showed that when a city doubles in size, it requires an increase in resources of only 85 percent. ... the average Manhattanite emits 14,127 fewer pounds of carbon dioxide annually than someone living in the New York suburbs."
In addition to universal mathematical proof that larger cities anywhere in the world are simply more efficient in resource management (something that many already knew for decades with more localized data), West shows that economic and innovation benefits accelerate in an identical manner due to increased human infrastructure of social networks:
"every measure of economic activity, from construction spending to the amount of bank deposits, increases by approximately 15 percent per capita"
It's not just better sustainability and greater numbers of patents. Negatives are also represented by these laws describing cities in their current modern form:
"After a city doubles in size, it also experiences a 15 percent per capita increase in violent crimes, traffic and AIDS cases"
So far no city has shown a certain maximum point in population after which rise in population shows increasingly diminishing and then negative returns. Neither has any megapolis shown population related rises in neurosis, anxiety, stress, crime, or NYC level of income inequality reaching a point where the city begins to collapse. The flight from American cities in the 60s and 70s into suburbia is not a historical demonstration of such a point. Post-flight population decreases in many cities and corresponding economic downturns prove West's laws. Obviously race related tensions or violence can cause a population to decline but population rise in itself did not cause the flight into suburbia. Many cities currently are far larger in population than they were in the 60s.
How can then we talk of "ideal city population size"? Isn't the sky the limit? Why not say that the ideal size is 5 or 10 million so we can more effectively drain the countryside of people and create sustainable engines of economic growth. Perhaps the rise in neurosis/stress can be collectively dealt with and crime and traffic managed the way Singapore and London do it? London copied Singapore's experience of charging cars more money the closer they drive towards city center for instance. And with the highest per capita CCTV camera rate in the world it's not hard to envision cities like London eventually turning into an oriental style police state where dropping chip bags on the sidewalk nets you an automatic and severe penalty. Taken to greater extremes, anti-anxiety prescription drugs can of course help segments of population most susceptible to stress inducing effects of overcrowding.
This points to another reason to search for optimal city population size. Namely, to not have a population so large that it now suffers from attempted solutions that deal with ills of overcrowding. It may be possible to turn a 30 million person megapolis into a super clean, regimented, policed, artificial mall like environment but which now suffers from new issues. Issues such as those 15% economic benefits from city doubling now partially neutralized on constant quality of life expenditures to combat neurosis and issues of new psychological ailments of living in a cramped artificial environment. Anomie, lack of sense of community, and alienation do not really disappear if densely cramped megapolis is scrubbed clean and has a policeman on every corner. For all the declining homicide rate in NYC, the city is more socially fragmented than ever.
This means not a dense urban core transitioning to less dense layers that ultimately transition to endless sprawl. Having written about sheer energy inefficiency of suburbia before and how experimental satellite cities tend to be positioned within nature (so inhabitants can walk from the urban core and find themselves in a surrounding forest), it makes sense to view an ideal city population size as being within an area that excludes sprawling low density edges. That is not to say that a city should not have a core of some sort but just that if a core is 5,000 people per sq kilometer then the city remains at 1,000-2,000 people per sq km at the edges and does not drop to village level of 200 per sq km. The actual layout can vary greatly. It can have a main core or be decentralized from the start by having multiple cores on the city edges as well as in the middle to more evenly spread the population. The lay out would of course be determined by the city's planned purpose if it has one (creating a purpose during initial city planning stages can aid in control of total population as well as help in achieving larger societal goals such as reindustrialization through science cities).
Migrations into cities and growth in their size is driven primarily by economic reasons and not by land scarcity or overpopulation reasons (see figure 1). People always underestimate how much livable land is on the planet's surface. That is not to say that we need to re-invent the suburban sprawl so everybody gets a shot at a backyard (which is theoretically possible albeit with a planetary ecological collapse likely given current resource management). What's essential to keep in mind is that ant hive cities of 10+ million do not necessarily have to be a part of necessary future development for all the world's people. Developing societies with favorable human to land ratios like Brazil and Nigeria may do well with clusters of 250,000-500,000 planned green cities. China appears to understand this even as it accommodates growth of dozens of 1 million + cities a year. Whichever techniques Beijing pioneers (for preplanned green city development) will then be readily copied by countries a lot more pressed in need for them such as Pakistan, Indonesia, India, and Bangladesh.
|Figure 1. Overpopulation is a myth|
Problems in political governance as a population ceiling.
So far we still got more pros pushing towards larger city sizes. Larger population making a city a more efficient engine of economic wealth generation and development sounds like an argument most people will side with at the end of the day. It seems hard to argue against the inertia and emulation of urban centers like London and Paris on the basis of psychologically uncomfortable overcrowding. This leaves more intangible values of effective political management and feelings of political empowerment.
So far the best governed countries in the world appear to be less than 10 million people each and primarily clustered in Northern Europe. They also have the best standards of living in the world and make a strong case that populations of entire sovereign countries should be limited to 10-20 million people. Their largest cities of Helsinki, Copenhagen, Stockholm, Zurich all fall under a million people and consistently rank in the top of livability indexes for urban areas. Obviously when you got a population of Sweden crammed within an area on which NYC sits, the people will not exactly feel a connection to their government. What use is an urban core being an efficient generator of wealth if that wealth is poorly managed and just flows through or out of it? Local governments are the last bastions of peoples will in the Western world and a city of under a million still allows some expression of it. National governments have become too distant, inaccessible, and corporately controlled for most populations of the planet and will remain increasingly so until technology allows some form of direct democracy later in this century. This leaves the city as a political unit that can still be sort of managed from below. Population size comes into play here as a limiting factor to how much simple people can accomplish and communicate to the authorities.