Urbanization:

Urbanization is a population shift from rural to urban areas, "the gradual increase in the proportion of people living in urban areas", and the ways in which each society adapts to the change. It is predominantly the process by which towns and cities are formed and become larger as more people begin living and working in central areas. The United Nations projected that half of the world's population would live in urban areas at the end of 2008 It is predicted that by 2050 about 64% of the developing world and 86% of the developed world will be urbanized.

That is equivalent to approximately 3 billion exurbanites by 2050, much of which will occur in Africa and Asia Notably, the United Nations has also recently projected that nearly all global population growth from 2015 to 2030 will be absorbed by cities, about 1.1 new exurbanites over the next 15 years Urbanization is relevant to a range of disciplines. including geography, sociology, economics, urban planning, and public health. The phenomenon has been closely linked to modernization, industrialization, and the sociological process of rationalization. Urbanization can be seen as a specific condition at a set time (e.g. the proportion of total population or area in cities or towns) or as an increase in that condition over time. So urbanization can be quantified either in terms of, say, the level of urban development relative to the overall population, or as the rate at which the urban proportion of the population is increasing. Urbanization creates enormous social, economic and environmental changes, which provide an opportunity for sustainability with the “potential to use resources more efficiently, to create more sustainable land use and to protect the biodiversity of natural ecosystems.”

Urbanization is not merely a modern phenomenon, but a rapid and historic transformation of human social roots on a global scale, whereby predominantly rural culture is being rapidly replaced by predominantly urban culture. The first major change in settlement patterns was the accumulation of hunter-gatherers into villages many thousand years ago. Village culture is characterized by common bloodlines, intimate relationships, and communal behavior whereas urban culture is characterized by distant bloodlines, unfamiliar relations, and competitive behavior. This unprecedented movement of people is forecast to continue and intensify during the next few decades, mushrooming cities to sizes unthinkable only a century ago.Today, in Asia the urban agglomerations of Osaka, Karachi, Jakarta, Mumbai, Shanghai, Manila, Seoul, and Beijing are each already home to over 20 million people, while Delhi and Tokyo are forecast to approach or exceed 40 million people each within the coming decade. Outside Asia, Mexico City, São Paulo, New York, Lagos, Los Angeles, and Cairo are, or are already, home to over 20 million people.

History:

From the development of the earliest cities in Mesopotamia and Egypt until the 18th century, an equilibrium existed between the vast majority of the population who engaged in subsistence agriculture in a rural context, and small centres of populations in the towns where economic activity consisted primarily of trade at markets and manufactures on a small scale. Due to the primitive and relatively stagnant state of agriculture throughout this period the ratio of rural to urban population remained at a fixed equilibrium.

With the onset of the agricultural and industrial revolution in the late 18th century this relationship was finally broken and an unprecedented growth in urban population took place over the course of the 19th century, both through continued migration from the countryside and due to the tremendous demographic expansion that occurred at that time. In [[England] population jumped from 17% in 1801 to 72% in 1891 (for other countries the figure was: 37% in France, 41% in Prussia and 28% in the United States).

From the development of the earliest cities in Mesopotamia and Egypt until the 18th century, an equilibrium existed between the vast majority of the population who engaged in subsistence agriculture in a rural context, and small center of populations in the towns where economic activity consisted primarily of trade at markets and manufactures on a small scale. Due to the primitive and relatively stagnant state of agriculture throughout this period the ratio of rural to urban population remained at a fixed equilibrium.

With the onset of the agricultural and industrial revolution in the late 18th century this relationship was finally broken and an unprecedented growth in urban population took place over the course of the 19th century, both through continued migration from the countryside and due to the tremendous demographic expansion that occurred at that time. In [[England] population jumped from 17% in 1801 to 72% in 1891 (for other countries the figure was: 37% in France, 41% in Prussia and 28% in the United States).

Causes :

Urbanization occurs as individual, commercial flight social and government action reduce the time and expense of commuting and transportation and improve opportunities for jobs, education, housing, and transportation. Living in a city can provide opportunities of proximity, diversity, and marketplace competition. As against this, there may be alienation issues stress, increased cost of living, and negative social aspects that result from mass marginalization Sub urbanization, which is happening in the cities of the largest developing countries, may be regarded as an attempt to balance these negative aspects of urban life while still allowing access to the large extent of shared resources. In cities, money, services, wealth and opportunities are centralized. Many rural inhabitants come to the city to seek their fortune and alter their social position. Businesses, which provide jobs and exchange capital, are more concentrated in urban areas. Whether the source is trade or tourism, it is also through the ports or banking systems, commonly located in cities, that foreign money flows into a country.Many people move into cities for the economic opportunities, but this does not fully explain the very high recent urbanization rates in places like China and India. Rural flight is a contributing factor to urbanization. In rural areas, often on small family farms or collective farms in villages, it has historically been difficult to access manufactured goods, though the relative overall quality of life is very subjective, and may certainly surpass that of the city. Farm living has always been susceptible to unpredictable environmental conditions, and in times of drought, flood or pestilence, survival may become extremely problematic.

Economic Effect:

As cities develop, effects can include a dramatic increase and change in costs, often pricing the local working class out of the market, including such functionaries as employees of the local municipalities. For example, Eric Hobsbawm's book The age of revolution: 1789–1848 (published 1962 and 2005) chapter 11, stated "Urban development in our period [1789–1848] was a gigantic process of class segregation, which pushed the new labouring poor into great morasses of misery outside the centres of government and business and the newly specialized residential areas of the bourgeoisie. The almost universal European division into a 'good' west end and a 'poor' east end of large cities developed in this period." This is likely due the prevailing south-west wind which carries coal smoke and other airborne pollutants downwind, making the western edges of towns preferable to the eastern ones. Similar problems now affect the developing world, rising inequality resulting from rapid urbanization trends. The drive for rapid urban growth and often efficiency can lead to less equitable urban development. Think tanks such as the Overseas Development Institute have proposed policies that encourage labor-intensive growth as a means of absorbing the influx of low-skilled and unskilled labor One problem these migrant workers are involved with is the growth of slums. In many cases, the rural-urban low skilled or unskilled migrant workers, attracted by economic opportunities in urban areas, cannot find a job and afford housing in cities and have to dwell in slums.

Urban problems, along with infrastructure developments, are also fueling sub-urbanization trends in developing nations, though the trend for core cities in said nations tends to continue to become ever denser. Urbanization is often viewed as a negative trend, but there are positives in the reduction of expenses in commuting and transportation while improving opportunities for jobs, education, housing, and transportation. Living in cities permits individuals and families to take advantage of the opportunities of proximity and diversity. While cities have a greater variety of markets and goods than rural areas, infrastructure congestion, monopolization, high overhead costs, and the inconvenience of cross-town trips frequently combine to make marketplace competition harsher in cities than in rural areas.In many developing countries where economies are growing, the growth is often erratic and based on a small number of industries.

For young people in these countries barriers exist such as, lack of access to financial services and business advisory services, difficulty in obtaining credit to start a business, and lack of entrepreneurial skills, in order for them to access opportunities in these industries. Investment in human capital so that young people have access to quality education and infrastructure to enable access to educational facilities is imperative to overcoming economic barriers.

Environmental Effect:

The existence of Urban heat islands has become a growing concern over the years. An urban heat island is formed when industrial and urban areas produce and retain heat. Much of the solar energy that reaches rural areas is consumed by evaporation of water from vegetation and soil. In cities, where there is less vegetation and exposed soil, most of the sun's energy is instead absorbed by buildings and asphalt; leading to higher surface temperatures. Vehicles, factories and industrial and domestic heating and cooling units release even more heat. As a result, cities are often 1 to 3 °C (1.8 to 5.4 °F) warmer than surrounding landscapes.Impacts also include reducing soil moisture and a reduction in reabsorption of carbon dioxide emissions.

The occurrence of eutrophication in bodies of water is another effect large urban populations have on the environment. When rain occurs in these large cities, the rain filters down the pollutants such as CO2 and other green house gases in the air onto the ground below. Then, those chemicals are washed directly into rivers, streams and oceans, causing a decline in water quality and damaging marine ecosystems.

First, the birth rate of new urban dwellers falls immediately to replacement rate, and keeps falling, reducing environmental stresses caused by population growth. Secondly, emigration from rural areas reduces destructive subsistence farming techniques, such as improperly implemented slash and burn agriculture.

In July 2013 a report issued by the United Nations Department of Economic and Social Affairs warned that with 2.4 billion more people by 2050, the amount of food produced will have to increase by 70%, straining food resources, especially in countries already facing food insecurity due to changing environmental conditions. The mix of changing environmental conditions and the growing population of urban regions, according to UN experts, will strain basic sanitation systems and health care, and potentially cause a humanitarian and environmental disaster

Health Effect:

In the developing world, urbanization does not seem to translate into a significant increase in life expectancy Rapid urbanization has brought increased mortality from non-communicable diseases associated with lifestyle, including cancer and heart disease Differences in mortality from contagious diseases vary depending on the particular disease.

Urban health levels are better in comparison those in rural areas on average. However, residents in poor areas such as slums and informal settlements suffer "disproportionately from disease, injury, premature death, and the combination of ill-health and poverty entrenches disadvantage over time." Many urban poor have difficulty accessing health services due to an increasing requirement to pay for them; so people resort to less qualified and unregulated providers.While urbanization is associated with improvements in public hygiene, sanitation and access to health care, it also entails changes in occupational, dietary and exercise patterns. It can have mixed effects on health patterns, alleviating some problems and accentuating others. For instance, in children urbanization is associated with a lower risk of under nutrition but a higher risk of overweight. Overall, body mass index and cholesterol levels increase sharply with national income and the degree of urbanization. Easier access to non-traditional foods may lead to less healthy dietary patterns. In India prevalence of diabetes in urban areas appears to be more than twice as high as in rural areas. In general, major risk factors for chronic diseases are more prevalent in urban environments

Changing Form :

Different forms of urbanization can be classified depending on the style of architecture and planning methods as well as historic growth of areas In cities of the developed world urbanization traditionally exhibited a concentration of human activities and settlements around the downtown area, the so-called in-migration. In-migration refers to migration from former colonies and similar places. The fact that many immigrants settle in impoverished city centres led to the notion of the "peripheralization of the core", which simply describes that people who used to be at the periphery of the former empires now live right in the centre. Recent developments, such as inner-city redevelopment schemes, mean that new arrivals in cities no longer necessarily settle in the centre. In some developed regions, the reverse effect, originally called counter urbanization has occurred, with cities losing population to rural areas, and is particularly common for richer families. This has been possible because of improved communications, and has been caused by factors such as the fear of crime and poor urban environments. It has contributed to the phenomenon of shrinking cities experienced by some parts of the industrialized world.

When the residential area shifts outward, this is called suburbanization. A number of researchers and writers suggest that suburbanization has gone so far to form new points of concentration outside the downtown both in developed and developing countries such as India. This networked, polycentric form of concentration is considered by some emerging pattern of urbanization. It is called variously exurbia, edge city (Garreau, 1991), network city (Batten, 1995), or postmodern city (Dear, 2000). Los Angeles is the best-known example of this type of urbanization. Interestingly, in the United States, this process has reversed as of 2011, with "re-urbanization" occurring as suburban flight due to chronically high transport costs.

conclusion : 

• the challenge facing the world today is to minimize the negative effects and build the benefits.
• infrastructure needs to be improved.
• opportunities should be created within rural areas to prevent migration to cities.  

video :

• http://ed.ted.com/lessons/urbanization-and-the-future-of-cities-vance-

• kitehttps://www.youtube.com/watch?v=IHoayVYfTVU