I. Urbanization: conceptual and measurement issues, temporal and spatial perspectives and the driving forces

A. Conceptual and measurement Issues

Simply defined, urbanization is the process of growth in the proportion of the population living in urban areas. It is distinguishable from the term "urban growth" which refers to the proportionate growth of urban areas themselves, that is, annual net additions to urban population divided by the size of the urban population (Preston, 1982: 650). To clarify, "growth of the urban population can be looked at in two ways: on its own, in which it is described as urban growth, and as a proportion of the national population, in which the term urbanization is used" (Oucho and Gould, 1993: 275).

The point to stress here is that in spite of the United Nations stipulation, there is no universally accepted urban centre threshold in both developed and developed countries. It has however, been established that while urbanization in developed countries has been supported by industrialization, including a substantial manufacturing base, in the developing countries it is supported by the service sector which compensates for the deficit of the manufacturing sector. Against this consideration, the rest of this section analyses trends, features and characteristics, patterns and the driving forces of urbanization. These are examined not only globally, but also with respect to the world regions defined in demographic terms as Africa, Asia, Europe, the former Soviet Union, Latin America (including the Caribbean), North America and Oceania.

B. Trends of urbanization

Urbanization trends may be best appreciated by examining the degree of urbanization in terms of indices such as the "proportion urban", the rate of urbanization and the rate of urban population growth over a specified period of time. Cities are currently absorbing two thirds of the total population increase in the developing world. At this rate, close to 2 billion people will populate the urban areas of developing countries by the year 2000, with some 600 million of this number being added during the current decade alone. Another 2 billion people are expected to be added to the urban population of the developing countries between 2000 and 2025: moreover, the majority of these new urban residents will be living in large cities. Today, half of the population is located in some 360 cities of over half a million inhabitants each. In 1950, the world's total urban population was 734 million, of whom 448 million were in the developed countries and 286 million in developing countries. The share between the two changed in 1980 when the developing countries made up 958 million of the world's total urban population of 1.8 billion. At the close of this century, this proportion is expected to gallop to 2.3 billion out of the world's total of 3.2 billion and by the year 2025 the developing countries will have 4.4 billion of the world's total urban population of 5.5 billion (United Nations, 1990a). Figure I indicates urbanization trends for the world, developed and developing countries, as well as for the major world regions for the period 1970-2035.

Estimates and projections suggest that during the 75 years from 1950 to 2025 the proportion of the world's urban population will have doubled, while the absolute world population will have increased nearly sevenfold. It is evident that the developing countries are urbanizing faster than the developed countries. This is a result of the rapid population growth in developing countries, which triggers demographic forces responsible for rapid urbanization (see figure 1). In respect of the world regions, Latin America is poised for the largest share of urbanization, followed by Europe. But Africa and Asia will have the smallest share, although they are expected to register much faster urban growth.

Figure 1a. World urbanization trends by regions, 1970-2025

Figure 1b. World urbanization trends by regions, 1970-2025

Source of data: World Urbanization Prospects 1990, (New York Nations, 1990)

During 1985- 1990 the growth rate of the world's urban population was 3.1 per cent per year (0.8 per cent in the developed countries and 4.5 per cent in the developing countries). Although the growth rate for the developing world peaked in 1980- 1985 at 4.6 per cent per year, it is now estimated to be declining (World Health Organization, 1993: 3). Currently, Africa exhibits the highest urban population growth rates, projected to persist up to the year 2000 and beyond. The projected scenarios are higher, but declining growth rates in the developing regions, which will contrast sharply with the already declining growth rates (expected to plummet further) in the developed world. Yet it must be stressed that the projected declines in growth rates will be occurring in the context of much larger urban populations thereby compounding urban problems. Of the 23 countries with the highest rates of urbanization in the range of 3.0 and 7.9 per cent per annum, 18 are in Africa alone, the rest being in Asia. Conversely, of the 25 countries with the lowest urbanization rates (-0.9 - 0.3 per cent per annum), 10 are in Europe, 9 in Asia, 2 in North America, 2 in Asia and I apiece in Africa and Latin America. From this account, it is evident that urbanization of the future will be an African phenomenon, given that African cities or agglomerations are yet to reach the sizes of their Asian or Latin American counterparts.

C. Demographic driving forces

Demographic studies of urbanization have identified rural-urban migration (and even immigration), natural increase of population and reclassification (involving either expansion or contraction of the urban locality) as the main driving forces underlying changes in urban areas. The universality of these components of urban growth has been clearly observed, although their mix differs by regions or countries. The contribution of migration to urbanization, though significant, has been exaggerated in many countries, particularly in developing countries where the high natural increase yields a youthful population which augments urban populations and which is exceptionally prone to migration. A case in point is sub-Saharan Africa where the first post-independence decade witnessed massive rural-urban migration which accelerated urbanization and where, recently, natural increase has taken over, reinforced by indiscriminate re-classification of formerly rural territory in some countries (Oucho and Gould, 1993: 280-281). Table I summarizes the situation between 1980 and 2005. In 1980-1985 natural increase accounted for a larger share of urban growth globally, in the more developed countries, North America, the former USSR and Africa; it was overwhelming in Oceania. Only in the less developed countries, Europe and Asia was the combined contribution of migration and re-classification more significant. Although the same pattern is projected to obtain in 1990- 1995, the contribution of migration and reclassification is expected to increase (or be equal with that of natural increase in 1990- 1995), and the two components are projected to dominate in the more developed countries, Europe and Asia in 2000-2005. implications of this changing picture for population management and quality of life must concern the United Nations, its regional commissions, national governments and individual urban areas and agglomerations. But these figures conceal intra-regional and national estimates and projections.

D. Policy-related determinants

In many countries, policy-related factors have given impetus to urbanization. Policy guidelines in different countries range from explicit urban policies or implicit socio-economic policies that influence urbanization, to settlement policies (which have been partly responsible for population decline in large cities) and urban hierarchy policies recognizing urban areas as growth/service centres; in some countries public services and environmental goals are pertinent elements of urbanization policy (Korcelli, 1982: 657). Most of these policies are aimed at avoiding hyper-urbanization (especially of primate cities), encroachment on agricultural land by urban areas and dispersal of population from metropolitan and peripheral regions of a country.

Table 1. Components of urban growth by country, or area, 1980-2005 (percentage of urban growth)

Note: The contribution of natural is calculated by assuming that die urban population has The same rate of natural increase as die national or regional population. The category of migration and reclassification is calculated as a residual. For details on the "urban component method", see Arriaga (1975).

Source: United Nations (1990) World Urbanization Prospects 1990, table 6, p. 27.

Empirical evidence suggests that the determinants of urban growth already discussed permit identification of three successive stages, especially in the third world: first, an early stage characterized by low urbanization when both rates of urban and rural natural increase are moderately high, and when migration contributes to urban growth more than natural increase; secondly, an intermediate stage characterized by less migration, and urban growth is largely attributed to natural increase and, thirdly, a late stage whereby high levels of urbanization and low rates of natural increase are experienced, and when migration takes over once again (Oberai, 1989: 4-5). There is, however, no rule of thumb for the three stages to be realized that systematically, as conditions differ by regions and countries and oscillations precipitated by non-demographic factors sometimes determine urbanization trends.

Apart from those forces discussed in this section, there are others, such as the pace of rural development, which depend largely on the ability of the agricultural sector to absorb or repel population. For instance, while in the Sahel region of Africa hostile climate resulting in drought has caused rural out-migration, in Latin America unequal distribution of landownership ranks among other repellents sparking off ruralurban migration (Oberai, 1989: 6). In both cases, urbanization is spurred by the weakened absorptive capacity of rural areas.

Figure 2. World's 30 largest urban agglomeration by population size in millions. 1950. 1970. 1990. 2000

Source. United Nations (1990) World Urbanization Prospects 1990 (New York, United Nations), table A,. 10. pp. 184-185