•Urbanization is the increase over time in the population of cities in relation to the region's rural population.(new world encyclopedia)•The increasing share of a nation's population living in urban areas (and thus a declining share living in rural areas).•The term urbanization is also used for the expansion of urban land uses.•It moves populations from traditional rural environments with informal•political and economic institutions to the relative anonymity and more formal•institutions of urban settings.

•Urbanisation was first started in United States of America•During the American colonial period, cities along the eastern seaboard were the centers of commerce and politics, thus urbanization began there • Boston, New York, and Philadelphia were the three largest cities in population size. Yet they were tiny in comparison to their size today. In 1790, the year after George Washington became the first president of the new nation, New York’s population was only 33,131; Philadelphia’s was 28,522; and Boston’s was 18,230 .•Today, of course, cities of this size are called small towns. New York’s population is vastly higher, at about 8.2 million; Philadelphia’s is 1.5 million; and Boston’s is 618, 000.

• US cities became more numerous and much larger during the nineteenth century because of two trends.• The first was immigration, as waves of immigrants from Ireland and then Italy and other nations began coming to the United States during the 1820s. •The second was industrialization, as people moved to live near factories and other sites of industrial production.• These two trends were momentous: People crowded together as never before, and they crowded into living conditions that were often squalid.

•American cities grew even more rapidly after the Civil War as both industrialization and immigration continued. By the early years of the twentieth century, US cities on the East Coast were almost unimaginably crowded

Global Urbanization•If the United States has urbanized during the last two centuries, so has much of the rest of the world. •Only 3 percent of the world’s population lived in urban areas in 1800.• By a century later in 1900, 14 percent of the world’s population lived in urban areas, and twelve cities had populations over 1 million. •Just a half-century later in 1950, the world’s urban population had doubled to 30 percent, and the number of cities over 1 million grew six times to eighty-three cities.•Today, more than half the world’s population lives in urban areas, and the number of cities over 1 million stands at more than four hundred. •By 2030, almost two-thirds of the world’s population is projected to live in urban areas. •The number of megacities—cities with populations over 10 million—rose from three in 1975 to sixteen in 2000, and is expected to reach twenty-seven by 2025

•Spread of education•Modernization•Change in Dress habits.•Adoption of modern Technology•Enlightenment of women.•Modern transport and communication. E.g.: Cell phones have become common even among rural people.•Active involvement in politics.•Growth of infrastructure like Banks, Post office.•Awareness among rural consumers.• Increasing demand for sophisticated products like cosmetics etc.

[A] IMPACTS ON THE ATMOSPHERE AND CLIMATE

1. The creation of heat islandMaterials like concrete, asphalt, bricks etc absorb and reflect energy differently than vegetation and soil.Cities remain warm in the night when the countryside has already cooled.

2.Changes in Air QualityHuman activities release a wide range of emissions into the environment including carbon dioxide, carbon monoxide, ozone, sulfur oxides, nitrogen oxides, lead, and many other pollutants.

3. Changes in Patterns of Precipitation Cities often receive morerain than the surrounding countryside since dust can provoke the condensation of water vapor into rain droplets.

[B] IMPACTS ON THE LITHOSPHERE AND LAND RESOURCES1. Erosion and other changes in land qualityRapid development can result in very high levels of erosion and sedimentation in river channels.

2. PollutionPollutants are often dispersed across cities or concentrated in industrial areas or waste sites. Lead-based paint used on roads and highways and on buildings is one such example of a widely dispersed pollutant that found its way into soil. Burying tremendous amounts of waste in the ground at municipal and industrial dumps

[C] IMPACTS ON THE HYDROSPHERE AND WATER RESOURCES1. Flow of Water into StreamsNatural vegetation and undisturbedsoil are replaced with concrete, asphalt, brick, and other impermeable surfaces. This means that, when it rains, water is less likely to be absorbed into the ground and, instead, flows directly into river channels.

2.Flow of Water through StreamsHigher, faster peak flows change streams channels that have evolved over centuries under natural conditions. Flooding can be a major problem as cities grow and stream channels attempt to keep up with these changes.

3. Degraded Water Quality The water quality has degraded with time due to urbanization that ultimately leads to increased sedimentation there by also increasing the pollutant in run-off.

D] IMPACTS ON THE BIOSPHERE1. Modification of HabitatsThe fertilizers that spread across lawns finds its way into water channels where it promotes the growth of plants at the expense of fish.The waste dumped into streams lowers oxygen levels during its decay and cause the die-off of plants and animals.

2. Destruction of HabitatsThere is also complete eradication of habitats as an outcome of Urbanization and native species are pushed out of cities.

3. Creation of New HabitatsNew habitats are also created for some native and non-native species.Cities also create habitats for some species considered pests, such as pigeons, sparrows, rats, mice, flies and mosquitoes. Urbanization has, for example, eliminated many bat colonies in caves, but has provided sites such as bridges for these species to nest.

Census 2011: Tamil Nadu 3rd most urbanized state

CHENNAI: More people in Tamil Nadu have moved from rural to urban areas the last 10 years compared to other states, according to the 2011 Census data. Tamil Nadu tops the list of urbanised states with 48.45% of its population living in urban areas , followed by Kerala, Maharashtra and Gujarat.

In the last 20 years, the rate of urbanization in Tamil Nadu has been rapid. According to the 1991 Census, only 34.15% of the total population in Tamil Nadu was classified as urban but in 2011, it has risen to 48.45%, an increase of 14.3%. Since the 2001 census, the percentage of urban population has risen by 4.41%.

"In Tamil Nadu, between 1991 and 1996 many rural areas have been reclassified as urban after the 74th amendment to the Constitution . This could be one reason for more people now living in urban areas," said Karen Coelho, assistant professor, Madras Institute of Development Studies, who specialises in urban anthropology.

•Urbanization is referred to as “necessary evil”•Instead of migrating to cities, developing the rural areas is a better option•Increase the educational and job facilities in rural areas•At least the rate of migration should b reduced•Recycling of all non renewable resources have to be encouraged to meet the increasing demand•The clearing of many slums and a huge increase in adequate housing for low-income individuals