The world’s urban population today is around 3.2 billion people¹ ― more than the world’s total population in 1960. During the 20th century, the urban population increased more than ten-fold. Today, half of the world’s population lives in urban centres,² compared to less than 15 per cent in 1900.³ Many aspects of urban change in recent decades are unprecedented, including not only the world’s level of urbanization and the size of its urban population, but also the number of countries becoming more urbanized and the size and number of very large cities. Since 1950, many urban changes have been dramatic...

Two aspects of the rapid growth in the world’s urban population over the last 50–100 years are the increase in the number of large cities and the historically unprecedented size of the largest cities (Table 2 and Figure 3). Just two centuries ago, there were only two “million-cities” (cities with 1 million or more inhabitants) ― London and Beijing (then called Peking). By 1950, there were 75; by 2000, 380. A large (and increasing) proportion of these million-cities are in Africa, Asia and Latin America (see Table 2).

The average size of the world’s largest cities has also increased...

Although urbanization is acknowledged as one of the most significant changes taking place within low- and middle-income nations, there is surprisingly little detailed study of what causes or influences its scale and nature within each nation. Urban population statistics can show which urban centres grow rapidly (or grow slowly, stop growing or shrink), but they tell us nothing about why.

Understanding what causes and influences urban change within any nation is complicated. Consideration has to be given to changes in the scale and nature of the nation’s economy and its connections with neighbouring nations and the wider world economy ―...

Few large cities had their initial urban expansion guided by a rational plan ― and, for those few, plans were applied only to parts of the expansion, or the planning guidelines, rules and norms were only partially applied. The many factors influencing the location and initial development of cities include the availability of water, good location on transport routes (where river or sea transport may be important), the location of government (with government agencies and employees as potential sources of demand for goods and services), a healthy climate, rich agricultural lands and, especially in the past, defence. But the main...

All the above may be taken to imply insuperable problems for expanding cities, their regions and the global environment. But Box 5 highlights how cities actually have large potential advantages for ensuring universal provision of infrastructure and services, keeping down waste levels, re-using waste streams and de-linking a high quality of life from high levels of resource consumption (and greenhouse gas emissions). That cities have economies of scale, proximity and agglomeration that bring substantial benefits for most businesses is well known¹⁸³; less discussed are the economies of scale and proximity for public goods and services or the dis-economies caused by...

The world will certainly be more urbanized in 10–15 years time, and will have more large cities, including more mega-cities. But most nations will certainly have fewer urban dwellers than has been suggested by many projections made in the last 20–30 years. Most cities will also be considerably smaller than anticipated.

On large cities and mega-cities. There are good grounds for questioning whether a large proportion of the world’s urban population will ever live in cities of more than 5 million or more than 10 million inhabitants. This is for two reasons. First, most national economies are unlikely...

The problems that arise from rapid urban growth are not inherent to cities or to rapid urban growth. Nor are these problems the result of a lack of knowledge of how to address them, or of a lack of precedents that show how to do so ― although many city and municipal governments may lack trained personnel and the needed revenue base. The knowledge of how to install and maintain the infrastructure and services that underpin good-quality city environments has developed over the last 150 years ― and cities have many economies of scale and proximity to support this. Over...