Urbanization is the process by which an increasing proportion of the population lives in urban areas. The level of urbanization is the proportion of population living in urban areas. Urbanization must be distinguished from urbanism, a term referring to the style of life usually found in large urban centers. A prior issue in studies of urbanization is to determine what constitutes an urban area. In medieval Europe or China, it may have been easy to distinguish between towns–generally tight-knit settlements, often fortified by walls to enable them to be protected from attack–and rural areas. This is no longer the case, either in the developed or the developing world, largely because transportation improvements have made it possible for people to reside a considerable distance from their place of work.
Studies of urbanization are mostly forced to rely on the definitions of urban areas adopted in each country. These vary considerably, thus complicating inter-country comparisons. For example, some countries count all localities with 2,000 inhabitants or more as urban; others designate certain categories of administrative area as urban; still others use criteria such as population density and presence of certain urban facilities. Moreover, many areas, particularly those on the outskirts of large cities, are no longer easy to classify in terms of a rural-urban dichotomy. There is great diversity among areas defined as urban, and likewise among those defined as rural. It has been argued that a more complex breakdown of localities according to degree of urbanness or ruralness is needed.
In 1950 only 30 percent of the world's population was living in urban areas. By 2000 nearly half the population–some 47 percent–was urban. The second half of the twentieth century was therefore a highly significant period in the history of world urbanization.
Some Western countries had already reached a 50 percent level of urbanization in the second half of the nineteenth century. The United Kingdom led the way, reaching this level in 1851. Australia reached it shortly after 1901, Germany in about 1910, and the United States in about 1918. Such countries therefore have a long history of predominantly urban populations. Japan, some Gulf states, and some Latin American countries have been predominantly urban since the middle of the twentieth century, but most of the Asian and African countries that are predominantly urban at the beginning of the twenty-first century reached that status only in the last two or three decades of the twentieth century.
This does not mean that there is no tradition of urbanization in Asia and Africa. In Egypt and China, for example, urban traditions go back to antiquity. In Southeast Asia, cities were substantial in pre-colonial times and at least one fifth of the population of the Malay Peninsula was urban in the sixteenth century. Even in sub-Saharan Africa, generally thought of as lacking in urbanization before colonization by Europeans, the Yoruba towns in Nigeria were already substantial in the nineteenth century.
Nevertheless, by the middle of the twentieth century, there were sharp differences in levels of urbanization between, on the one hand, the entire continents of Europe and North America and countries of European settlement such as Argentina, Chile, Uruguay, Australia, and New Zealand, and, on the other hand, Asia, Africa, and the rest of Latin America. In Asia, only Japan and a few city-states and oil producers had reached 50 percent urbanization; in Africa, only some countries of the western Sahara. The general situation by continent is shown in Table 1.
Over the second half of the twentieth century, Latin America experienced an exceptionally rapid pace of urbanization, reaching European and North American levels by 2000. Eastern Europe, which had lagged behind the rest of Europe at mid-century, similarly caught up. In both of these regions, the
level of urbanization increased by more than 30 percent over this period. The pool of rural population from which rural-urban migrants can be drawn has been declining since 1950 in Europe and North America; in Latin America the rural population leveled off around 1985. Many urban centers in countries such as the United Kingdom, Ukraine, Spain, and Italy are actually declining in population. Japan and the Republic of Korea are also reaching this point.
But urbanization was a universal phenomenon in the late twentieth century. Throughout Africa and Asia there was a marked increase in urban proportions, and an even larger increase in the growth of the urban population, since urbanization was occurring in a period of historically unprecedented rates of overall population growth. So far, Africa and Asia have only reached the levels of urbanization attained in Latin America in the 1940s. Whether they will follow the very rapid urbanization that Latin America experienced over the 1950s and 1960s will depend on many factors, particularly the pace and style of economic development.
Percentage of Population Living in Urban Agglomerations
The proportion of the total population residing in truly large cities differs greatly across countries, but in general has been rising over time. Table 2 presents information for selected countries on trends in proportions residing in urban agglomerations of 750,000 or more in 1995. Differing definitions of the term urban raise problems of comparability for percentages of populations in urban areas, but this is less of a problem with data on urban agglomerations.
Over the period from 1950 to 1975, the proportion of population living in large cities increased in all the countries shown except the United Kingdom. However, in the period from 1975 to 2000, Italy, Australia, and Argentina also registered a fall in the proportion of the population living in large cities. This appears to reflect the phenomenon of counter-urbanization–the tendency in recent decades for population to be redistributed down the urban hierarchy, either through the absolute decline of the largest cities or through the faster growth of smaller urban places. Many Asian and African countries have much lower proportions of their population living in urban agglomerations (many of them below 20%), but this proportion has almost everywhere been rising over time.
In some countries, the largest city dominates the urban hierarchy, in many cases containing more than half of the total urban population. Many medium size and small countries demonstrate such "urban primacy." In the most populous countries such as China, India, the United States, or Brazil, however, one city is never dominant.
What Causes Urbanization?
The underlying explanation for urbanization involves changing employment opportunities as structural change takes place in the economy. The industrial and service sectors greatly increase their share of output during the course of economic development. Changes in employment structure also reflect increasing productivity in agriculture, which releases agricultural labor. Primary industry's share of employment thus can fall from as high as 70 percent to well below 10 percent. Since employment in secondary and tertiary industries is more heavily concentrated in urban than in rural areas, these structural changes are associated with urbanization.
Factors Contributing to City Growth and Overall Urban Growth
In accounting terms, there are three sources of population growth in urban areas: natural increase of the population living in urban areas, net migration from rural to urban areas, and reclassification of areas formerly defined as rural to urban. Though these three sources are neatly differentiated if calculated over short periods of time (perhaps up to one year), there is in fact considerable interaction between them over the medium to long term. Migrants increase the stock of urban dwellers whose balance of births and deaths makes up the natural increase of the urban population. The natural increase of the rural population increases the "pool" from which rural-urban migrants are drawn. Finally, reclassification is normally based on changes in the characteristics of localities, and increase in population density resulting from natural increase and net migration is frequently a major factor in modifying the characteristics of particular localities toward a more "urban" nature.
Studies by Samuel H. Preston (1979) and Martin Brockerhoff (1999) have examined the factors contributing to city growth over the period from 1960 to 1970, and in developing countries between 1970 and 1990, respectively. In the earlier period, there was an almost perfect association between national population growth rates and city growth rates, suggesting that the same forces fuel population growth in cities and in the countries where they are located. In the more recent period, however, a 1 percent increase in total population growth raises the size of the city population by a lesser percentage, suggesting (in light of continuing increases in urbanization) that smaller urban centers not included in the analysis have been growing more rapidly. In both periods, faster growth of national GDP per capita raised city growth rates, presumably through stimulation of demand for labor in urban industries.
Virtually all of the world's population growth between 2000 and 2030 is expected to take place in urban areas. During that period the urban population is expected to increase by 2 billion (from 2.9 billion to 4.9 billion), the same number that will be added to the population of the world. The growth rate of the urban population will average 1.8 percent per annum, a rate sufficient to cause a doubling in 38 years. Globally, the population of rural areas will remain roughly constant, reflecting a decline in rural populations of the developed countries offset by a continuing (though slowing) rural growth in developing countries. From 2020 to 2025, the rural population of developing countries will begin a steady decline, repeating the experience of the developed countries since 1950.
The level of urbanization is expected to continue increasing, even in the highly urbanized developed countries, where the urban population is expected to reach 84 percent in 2030. But the rise is likely to be much more rapid in Africa and Asia, which will both pass the 50 percent urban mark before 2025. Between 2000 and 2030, the urban population in Africa is expected to increase from 38 percent to 55 percent, and in Asia from 37 percent to 53 percent. Given that population growth rates are higher in Africa than in any other continent, the substantial rise in urbanization expected over the period implies very rapid increases in Africa's urban population over this period–over 3.5 percent per annum from 2000 to 2010, 2.6 percent from 2025 to 2030.
Very large cities–those with populations over 10 million–will continue to increase their share of the world's population, but only to a level of about 5 percent by 2015. United Nations demographers in the past have tended to overestimate the growth of large cities, and in recent years have made substantial downward adjustments to the population projections for many of them. On the other hand, the populations living in the "mega-urban regions" surrounding these cities are both larger and growing more rapidly than the populations in the official urban agglomerations, because the most rapid growth tends to be in areas outside the agglomeration limits.
Brockerhoff, Martin. 1999. "Urban Growth in Developing Countries: A Review of Projections and Predictions." Population and Development Review 25(4): 757–778.
Champion, Anthony. 2001. "Urbanization, Suburbanization, Counterurbanization and Reurbanization." In Handbook of Urban Studies, ed. Ronan Paddison. London: Sage.
Jones, Gavin W., and Pravin Visaria, eds. 1997. Urbanization in Large Developing Countries. Oxford: Clarendon Press.
Preston, Samuel H. 1979. "Urban Growth in Developing Countries: A Demographic Reappraisal." Population and Development Review 5(2): 195–215.
Tarver, James D. 1994. Urbanization of Africa: A Handbook. Westport, CT: Greenwood Press.
United Nations, Department of Economic and Social Affairs, Population Division. 2001. World Urbanization Prospects: The 1999 Revision. New York: United Nations.
Weber, Adna. 1963 . The Growth of Cities in the Nineteenth Century. Ithaca, NY: Cornell University Press.
Gavin W. Jones