Which is the world’s largest city?

For many years, Tokyo and Shanghai headed the world league table of the largest cities, but in the early 1980s Mexico City pulled ahead. Present forecasts suggest that it will have 30 million people by AD 2000. The expansion of Mexico City is part of a trend throughout developing countries for poor people to leave the hard life in the countryside and seek better opportunities in the cities.

In Mexico, 55 out of every 100 people lived in urban areas in 1965. By 1983, the figure had risen to 69. This trend is even more marked in some other nations. For example, the percentage of city dwellers in Brazil increased from 51 per cent in 1965 to 71 per cent in 1983. Many cities in developing countries do not have enough houses, jobs or social services for the new immigrants, so slums develop on the outskirts, and disease and crime become serious problems.