If the quality of a water source is so degraded that restoring its quality for further use is not feasible, then the source is lost for all practical purposes. The official report of the Kenya census of 1979 Kenya, 1982:64 , for example, concluded that the data on place of residence in 1978 was bedevilled by the biases that are liable to afflict all questions involving dating and reference periods in Africa…. This chapter describes the major characteristics, trends, and differentials, as well as the determinants of internal migration, urbanization, and population distribution, in sub-Saharan Africa by using available data and estimates for at least the last two decades 1970—1980 and 1980—1990 and projections for 1990—2000 and into the twenty-first century. Migration Selectivity and Differentials An important feature of any form of voluntary internal migration is the selectivity of migrants by demographic and socioeconomic characteristics from the general population. The Assam valley in the north-east and the Circars coast on the Bay of Bengal has moderate density of population although these areas receive heavy rainfall.
Per capita use decreased from 184 gpcd in 1990 to 179 gpcd in 1995 even though the nation's population increased by 7 percent during that period. Tropical forests, savanna, tundra and taiga provide different media for human occupation and concentration. Geographically, the research included a sample of rural communities from the NorthWestern Region of Romania. Yegorov 2005 Yegorov , 2009 elaborates the concept of the economic role of population density. Duration of human settlements is an important determinant of the magnitude of population concentration in any area. Several regions show a highly focal population distribution, with 90% of the population concentrated in less than 10% of the land surface, such as in South Africa, Namibia, and along the North and East coasts. It is the ratio of the observed mean nearest neighbor distance in the pattern to that expected for a Poisson point process of the same intensity.
However, they have not coalesced into any consensus on approaches or theoretical baselines. It first adopts an essentially spatial perspective in summarizing the geographical patterning of movement, emphasizing the mix of rural and urban sources and destinations, and then explores migration selectivity, in particular through sex, educational, and occupational differentials. Recent work showed that GlobCover was the global land cover dataset that, combined with detailed settlement extents, produced the most accurate population distribution data in an African context. In Kenya and Zaire, an urban area is a settlement with 2,000 or more inhabitants; in Ghana, the threshold is 5,000 inhabitants Ajaegbu, 1979:87. Future work will consider more sophisticated handling of these components of temporal uncertainty and its propagation through the projections. Natural resources are also necessary in order for people to survive. The bureau also reported that the doubling time from the year 2000 for the population of the United States, at its current rate of growth, is about 120 years, for the world 51 years, and for the less developed countries, including China, 36 years.
Definitive migration may be further subdivided into irregular movements, where neither the timing nor the destination of the next move is known characteristically in the case of refugees , and permanent movement, where the moves are considered by those involved to imply a permanent commitment to the new area of residence. The contemporary world no longer presents a picture of small isolated groups of human beings scattered over a vast territory, as Sumner described primitive society1. A poorly developed economy is often unable to support large populations and people end up living in poor housing e. The importance of these estimates can be seen when one notes that about 81 percent of the world's current population resides in less-developed countries. However, the income of farmers did not grow as fast as food price index. An exception in the 1980s, however, is Mazur 1984 on labor migration in Mali. Post-partition redistribution between India and Pakistan, or displacement of several million Sudanese as a result of civil war, or expulsion of Asians from Uganda in the early 1970s are some of the instances of how political events can cause changes in population patterns.
People must be able to obtain the raw materials necessary to build places in which to live and work. Competing Interests: The authors have declared that no competing interests exist. Limited job opportunities cause some areas to be sparsely populated e. The article focuses on one specific program implemented under the Cohesion policy in the framework of the National Plan for Rural Development, called Measure 322. It is generally said that the population map of India follows its rainfall map. A relatively simple mathematical model is proposed to explain the emergence of spatial pattern with heterogeneous density and phase transition between urban and rural areas.
In the world with low population density competition might not even emerge because even monopolist can become bankrupt due to low demand density, especially in the environment of high transport costs. The length of a border requires protection efforts and thus is a first type of cost. As Manchuria developed into the principal industrial region of China, however, large urban centres arose there, and the nature of the migration changed. As technological advances enable mankind to overcome limitations … of climate, people move in greater numbers into what would otherwise be marginal climatic areas. Yegorov 2009 shows that monopoly may not survive in the environment of low population density just because it may not be able to cover transport costs to all consumers, or consumer demand will be too low in its location to cover its fixed costs.
Other places where the climatic conditions are temperate and tropical tend to have a higher population concentration. Even in the area of models of African experience, however, there has been a general weakening of theoretical work in the face of a growing complexity of what is known about the migration experience throughout sub-Saharan Africa. The goal of this project is to model the global and local markets for natural gas, taking into account not only economic but also geopolitical and technological effects. The second factor that can decrease the size of a population is emigration. From this figure you can determine many features of a country e. Rising Himalayas, thus, mark the northern limit of dense population in the Ganga plain. Then at the equatorial cell they blow east to west again.
Estimates of sex ratios from censuses and surveys reveal high sex ratios i. With technological progress and increasing control over nature, man has been able to affect many of the influences of climatic conditions. In association with climatic conditions, varying soil types give rise to variety of vegetation cover on the earth surface. Abrupt changes in the density of population can be seen on the world map of population distribution where plains meet mountain ranges. Same geographic conditions provide different opportunities for people with different types and scale of economic activities.
The environmental factor in migration has not been given much prominence in recent years, as is evident in the lack of concern shown in the Nairobi conference papers and migration literature see Table 2. International labour movements take place when there is shortage of labour in one country and a surplus in other countries. Therefore the number of people in the world has grown rapidly. The principal distinction made is between circulation i. This is why large land masses such as Greenland and Antarctica are sparsely populated. Tatem 6 Department of Geography, University of Florida, Gainesville, Florida, United States of America, 7 Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America, 8 Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America, Figure S1: National travel time plots.
Since India is a tropical country, temperature is fairly high and does not play as important a role as is done by rainfall except in extreme cases. Therefore, most of the population is concentrated in the river valleys. Many countries have also experienced the growth of smaller centers, often as a result of administrative decentralization, as in the state capitals in Nigeria and, to a lesser extent, the regional capitals in Tanzania. A cursory look at the data indicates that, on average, population densities tend to be the lowest in middle Africa, where they range from 4 to 21. His approach may be a model for a great deal of migration analysis on this theme that may be needed in the coming years. Average per-person travel time to nearest settlement with more than 50,000 people, calculated by combining the global map of accessibility with our detailed population distribution dataset.