Forty-one percent of the world's population resided in urban areas in 1985: 72 per cent in the developed regions, 69 per cent in Latin America, and about 30 per cent in Africa and Asia.

The definition of urban areas differs from one country to another. The smallest places that are classified as urban range between 200 and 30,000 people. The process of urbanization, defined as an increase in the proportion of population living in urban areas, is largely a oneway process leading to a concentration in the pattern of population distribution.

The dynamics of population growth, industrialization, and agricultural modernization are expected to keep urban population growth rates above the rural growth rates in all regions. The urban population of developed countries is expected to rise from 71.5 per cent in 1985 to 74.8 per cent by the year 2010. In Africa, it is expected to increase from 31 to 41 per cent; in Asia (including Japan), from 28 to 35 per cent; and in Latin America, from 69 to 77 per cent. The number and size of "megacities" will increase rapidly in developing countries.

Despite the continuing exodus to urban areas, the population residing in rural areas still comprises a majority in most developing countries. Approximately one third of the total population increase in the developing countries in the 2000's will occur in rural areas. In the developed countries, the rural population accounted for less than 28 per cent of the total population in 1985, and it is projected that the share will fall to 25 per cent in the year 2010

The total rural population of the developing countries (including China) is expected to increase at an average annual rate of 1.24 per cent during the period from 1990 to 1995 and at 0.96 per cent per year between 1995 and 2010.  In Latin America, the growth of the rural population nearly halted after 1980. The size of its rural population (125 million in 1985) is projected to be practically unchanged through the first decade of the 21st century. Rural population growth in Africa, however, was about 2.1 per cent per year in the period from 1980 to 1985, and in Asia it was about 1.45 per cent per year. By the year 2010, the rural growth rate is projected to fall slightly in Africa, to about 1.8 per cent, and substantially in Asia, to about 0.8 per cent, due to migration and declining rates of natural increase. Nevertheless, the rural population will still comprise a large majority in these regions: Africa, 59 per cent; East Asia (including Japan), 67 per cent; and southern Asia (including Southeastern and Western Asia), 63 per cent.

Rural-to-urban migration is only one type of population movement within a country. There are movements from urban to rural areas, among urban areas and among rural areas. All types of migration are intimately related to social and economic changes and have significant policy implications. However, it is difficult to assess the situation, due to lack of statistical data.

An analysis of data from 57 countries, both developed and developing, indicates that the annual rate of net in-migration in urban areas (the number of in-migrants net of out-migrants divided by the urban population) ranged between 0.9 and 4.6 per cent in the developing countries and between 0.03 and 2.9 per cent among the developed countries. In Latin American countries and in the developed countries, there is a tendency for female rural-to-urban migrants to outnumber their male counterparts. Male migrants are relatively more numerous in Africa and Asia. Among the 57 countries surveyed, 24 had sex ratios of the migrants (number of males per too females) smaller than 80, while migrants in 10 countries had sex ratios over no. These migrants tend to be young. In the developing countries, around 25 per cent of the migrants were aged 15 to 24, and in the developed countries more than 20 per cent were in that age bracket; in some countries, the proportion was much higher. Another 20 to 40 per cent were children under the age of five.

From 2004, the definition of internal migration becomes a problem for European countries that are members of the enlarged European Community. Already there are moves on the part of the original members to put up barriers to what they envisage will be a mass movement of workers from east to west.