Azeem Azhar's recent newsletter, titled "Don't call time on the megacity: cities will learn and adapt," is a reminder of the tensions that cities face. There are forces of attraction. And there are also forces of repulsion.

Cities all around the world continue to create wealth and lift people out of poverty. But they also repulse people through traffic congestion, housing supply shortages, and overcrowding (which is distinct from density). Generally though, the forces of attraction have tended to outweigh the forces of repulsion, which is why the world continues to urbanize.

As Azeem points out, the first city believed to have reached 1 million inhabitants was Rome. It happened some 2,000 years ago. In the 1930s, New York then became the first city to reach 10 million inhabitants. And today, the 10 largest urban agglomerations in the world look something like this:

Outside of Japan, all of these city regions are expected to add many more people by 2030. Missing from this chart, however, are cities such as Lagos, Nigeria. Between 2018 and 2050, the UN estimates that 35% of the growth in the world's urban population will come from just three countries: India (+416 million), China (+255 million), and Nigeria (+189 million).

Long live the megacity.