There is a claim that more 50% of humankind live in cities. This claim, however, is wrong. The reason is that a city and an urban environment is not the same and the correct description would be that more than 50% live in urban environments.
This differentiation has a huge impact, Caracas, Mexico City and Jakarta have a continuous urban area that goes beyond the official city borders of each and result in abrupt policy changes along the administrative borders. For instance, Caracas has 5 different mayors and police forces and the mayor of Mexico City only covers 38% of the urban territory and Jakarta grew into most of its neighbouring towns and cities.
Cities in the tropical zone expand into the arable land and risk the food supply. The overlap of urban expansion with food production is a policy challenge. Changing agricultural land to real estate gives a short-term economic boost (to owners), but permanently damages the ground for agricultural purposes.
Urban discussions put forth by Yona Friedmann in the 60s already pointed out future migrations due to insufficient urbanisation. The collapse of urban environments due to (civil) war and bad economic circumstances have causes a large flow of migrants towards Europe that is remnant of Friedmann’s predictions. Migration challenges our consolidated models of cities. For instance, the Calais Jungle in France is a 30’000 people town with no formal infrastructure that epitomizes the challenge.
Shenzhen did not exist 30 years ago and now is the fourth-biggest city in China. It was a top-down decision by the Chinese Government to urbanize 250 million people and Shenzhen is one of the resulting cities. The urbanisation constitutes a migratory move.
Blue print cities have shown not to work properly, so the focus has moved to an iterative model that starts out with existing slums. The slums than get improved infrastructure until they are a functional city. In Latin America people have been brought into the vicinity of the city, creating slums. The slums are slowly transformed by introducing infrastructure. However, this poses many difficulties.
What is needed to create those cities is scale-less handling of the problem from a block in a quarter to the intercity areas. Hierarchical ordering of the problem is not sufficient to solve the problems (as shown by the past).
A provocative claim to close the introduction is that China is urbanising beyond their territory (in Africa, South-East-Asia and more).