Introduction

During recent decades, several less-developed countries have experienced relatively rapid economic growth rates. However the benefits of overall economic growth have been unjustifiably distributed in favour of a few localities, with large population sectors of each country remaining peripheral to such benefits. The process of development that generates the structural changes associated with socially- and morally-orientated productive and distributional systems is still in the infant stage.

A distinctive feature of an undeveloped country is the existence of a large subsistence sector embracing the majority of the population, characterized by low productivity, low income, lack of access to innovation and widespread disguised unemployment. This sector contrasts with the other sector, which combines small growth poles that are either urban or crop-producing centres. In such a dualistic setting, the heart of the development problem lies in the gradual shifting of human resources from the subsistence sector to the other sector (Fei and Ranis, 1963), resulting in the uneven distribution of population in a country. But as regards scale and tempo of population mobility, the share of urban centres in many developing countries is significantly larger than the share of crop-producing centres. The environmental contrast in these countries is particularly striking between urban and rural sectors, which activates the preponderance of urban-ward migration.

However, the unevenness of population distribution, or changes in the shape of its distribution over time, is not only a product of spatial mobility of people, but also of relative differences in rates of natural increase among regions in a country.