In this video, Wendover Productions asks some simple (if rarely asked) questions about cities: Why do they exist? What causes them to grow exponentially over time in the way they do? In answering these questions, the video suggests that, somewhat paradoxically, the creation and growth of cities is a natural phenomenon, bringing up some interesting implications regarding city planning in the future.

Wendover Productions explores the idea of Zipf’s Law, which states that within each country, the population of the second largest city will be around half of the population of the largest city, the population of the third largest city will be around a third of the population of the largest city, and so on. In other words, the population of a city is approximately inversely proportional to its rank. This mathematical phenomenon does not only hold true for the distribution of populations in cities, but also in various other parts of our world: the ranking of the most commonly used words, the diameter of moon craters, the popularity of opening chess moves—all of these seem to follow Zipf’s Law, with no definite answer to why. This suggests that the distribution of population density across the world follows natural laws, and this could play into the ways in which we make decisions about the design of our cities.

If we are aware that the "rank" of each city in a country has a low possibility of changing, how does that change our city planning?

The video describes cities as a result of "natural selection," in which humans chose the optimal place to live after a nomadic lifestyle was no longer necessary, and these settlements evolved into our cities. It suggests that the existence of cities follows the Principle of Least Effort, where people crowded into cities because dense populations are efficient at generating trade and income. If businesses are geographically close to one another, people will flock there in search of employment, which will then lead to businesses moving to these cities in order to be able to hire the best employees. This cyclic situation creates a common labor pool and more efficient trading and collaboration between companies.

In analyzing the possible correlation between wealth and urban population, the richest countries in the world were found to have the highest percentage of their population living in cities. Inversely, the countries with the lowest GDP were also those with some of the lowest rates of urbanization. Although these statistics do not show a perfect correlation, this fact nevertheless suggests that cities exist because they make wealth possible. Cities create efficiency, which in turn creates wealth.

So what does this mean for architects? The idea that population density could be an almost fatalistic, natural phenomenon gives us a starting point in how we look at cities and population growth. The video also touches on suburbanization, which has grown due to more widely accessible transportation methods. As the peripheries of our cities continue to grow and extreme high-density living becomes unavoidable, how can we change the way we analyze the growth of our cities and how we design for them?