In 1800 only 3% of the world's population lived in cities. By the end of the 20th century, 47% did so. In 1950, there were 83 cities with populations exceeding one million; but by 2007, this had risen to 468 settlements of more than one million people. If the trend continues, the numbers of people who live in cities with at least 500.000 inhabitants, will double every 38 years, researchers estimate.
According to calculations of the United Nations, today's urban population of 3.3 billion will rise to nearly 5 billion by 2030, when three out of five people will live in cities and more than 2 billion people will be living in slums. The increase in the number of megacities causes huge problems, especially in Africa and Asia. Scientists reckon that until 2030 urban growth will mostly take place in developing countries. As a consequence, housing conditions are often very poor.
Although most of the world's megacities are located in the developing world, there are three major reasons why the developed world should clearly to pay attention to them. First, because what happens there affects the rest of the world. Secondly, megacities are key instruments of social and economic development. Thirdly, they offer new market opportunities to both the developing and developed world.
Not always, but in a number of cases, a megacity is also the capital of a country or province.