Cities are perhaps the greatest human-made constructs. They have their good and bad characteristics. The bigger the cities, the more their good and bad characteristics strengthen their affect people. Cities have their physical lifelines. Physical flows of people, resources, and energy combined compose the metabolism of the cities. Cities look and feel different, but power laws affect them. These scaling relationships have hidden regularities. Ideas, such as patents and businesses in cities follow power laws too. If you are not familiar with power laws, you can learn about them here.
Power laws in cities are similar around the world
Power laws have the same scales around the world. For example, the amount of people living in the second biggest city in a country has about half the amount of people in the biggest city. And the third biggest city has about one-third of the people in the biggest city. Cities have national characteristics. The scale of different metrics depending on the culture, economy, and individuality of each national system. Scaling laws within the countries are similar, but the physical and mental flows differ between countries. If the biggest city in one country has 10 million people and the second biggest city has 5 million, then the biggest city in another country has 4 million people and the second biggest city has 2 million people.
15 percent rule
Cities have different power-law scales, but the most common and important exponent is 0.85 or 1.15 depending on which parameter is scaled. What 0.85 exponent means is that when the size of the city doubles you need 15 percent less of something else per capita to achieve a certain goal. 1.15 means that you will get 15 percent more of something per capita when the city size doubles. These exponents are common in the flow of resources and energy in cities. They are also common in social networks. When the city size quadruples, it needs only about 72 percent of something per capita and gets about 32 percent more of something per capita. Thus, the bigger the city the more efficient it becomes. Getting something more or less per capita isn´t always a bad or a good thing.
Bigger cities need less infrastructure per capita than smaller cities. Physical flows like roads, water and gas lines, and electrical networks all scale to 0.85. A city with 2 million people needs only 185 percent of the infrastructure compared to a city with a million people. The reason for this is that the end-users don´t have to build everything only to themselves. For example, gasoline stations need less space because the economy of scale affects it. Gasoline stations can have bigger gas supplies in a city because they have more potential customers living in the same area. Therefore, you need a smaller amount of them. Most of the physical infrastructure follows this double the size and needs 15 percent fewer resources per capita rule around the world. At least in places from where you can find official statistics about these parameters.
When the city size doubles, it produces 15 percent higher wages, more patents, more crimes, and more sexually transmitted diseases per capita. Most socioeconomic parameters follow this rule, including the speed of walking. These scaling laws make cities more efficient and people more productive in them. They also bring unwanted consequences, but most people in cities have better lives because of them. The best way to create greater nations is to enable the growth of their cities. Of course, nations should also focus on limiting the bad consequences of growing cities before they grow too big. The glorious past of the cities won´t guarantee a glorious future for them. The latter is just more probable consequence.
Some parameters don´t follow the 15 percent rule
Some parameters have a scaling exponent of close to one like the number of houses, and jobs per capita. Doubling the city size doubles the number of businesses. The diversity of the businesses stay pretty much the same. New kinds of businesses increase only by 5 percent when the city size doubles. What happens is that when some businesses become successful in a city, people living in it establishes new businesses that support the success stories. There are many other power-law exponents concerning cities. Let's forget them, at least for now.
There are limits to growth for cities. They don´t grow forever. When the maintenance costs in cities become too large, the growth stops. Maybe the biggest bottlenecks for the growth of the cities come from energy supplies. Growing cities need more energy. If the supply of energy can´t move as fast as they need for energy grows, growth will eventually stop. It also stops when the amount of people wanting to move to a city diminishes.
Understanding power laws is important if you want to understand the world. Power laws are more common than most people think. You can learn more about them from the book Scale, by Geoffrey West. I recommend you to read it.
-TT
No comments:
Post a Comment