Parallel to the growth of slums, gated communities – or exclusive neighbourhoods – are also on the rise. These are fenced and well-monitored communities in which affluent members live, further driving the trend towards separation among urban populations.

But it's not just living spaces splitting the cities – globally, there is a major push towards big new building projects like über-modern banks and business districts which stand in stark contrast to informal areas for the poor. These central business districts (CBD) are often siloed off from the main part of the city and migrate, along with the gated communities, towards the outskirts of town as is the case in Pudong, Shanghai and Beijing.

For the most part, urban planning is based on the needs of the consumer and culture-oriented upper classes and economic growth sectors with the result being that the gap between rich and poor continues to grow. Such fragmented cities are a fragile entity in which conflicts are inevitable.

Many condemned the initiative as thinly-veiled colonialism. But the current leaders of Honduras, one of the poorest countries in the Western Hemisphere and one of the most violent in the world, were receptive to Romer’s idea, feeling they had little to lose. They have begun laying down the legal groundwork for the plan. President Juan Orlando Hernandez won re-election in 2017 in a vote where the privatised cities plan was one of the central controversies.

But activists warn that the privatised enclaves will only worsen social inequality and undermine sovereignty in an already weak and deeply divided country.

How much sovereignty should poor countries like Honduras relinquish to chase foreign investment? Can cities, by definition the wellspring of civic spirit, flourish if their public institutions are privatised? Should someone own an entire city? And would you like to live in it?

Cities across the globe are expanding; but they are changing in other ways also, Hyett, continues: “As the urban population grows, emerging markets are experiencing rising incomes and cities in all parts of the world are witnessing an aging demographic trend. This means that social and cultural behaviors can change quickly and frequently. To stay on top of these trends it is essential to know what consumers in these markets need and want; city-level insight is now vital for understanding such developments.”



https://www.globaldata.com/importance-megacities-contemporary-economy

"The world is rapidly becoming urban. More than half the world’s 7-plus billion people live in urban areas (urban cores, suburbs and small towns). Nearly a quarter of the population lives in “cities” of a million or more. Eight percent reside in megacities — urban areas of at least 10 million. And that percentage rises with each new megacity."

"Urbanization has been occurring in the developed countries of the West for 200 years. Since the Industrial Revolution, a period from the 18th to 19th century in which machine-based manufacturing grew tremendously, cities have grown rapidly. As technological innovations flourished, economies previously dependent on manual labor and draft-animals began to change. People moved into the cities to find work and relatively quickly, cities began to grow exponentially."

"Optimists see a new network of powerful, stable and prosperous city states, each bigger than many small countries, where the benefits of urban living, the relative ease of delivering basic services compared to rural zones and new civic identities combine to raise living standards for billions. Pessimists see the opposite: a dystopic future where huge numbers of people fight over scarce resources in sprawling, divided, anarchic "non-communities" ravaged by disease and violence."

Megacities — cities with populations equaling or greater than 10 million people — are producing an unprecedented amount of air pollution, according to scientists at the American Chemical Society's annual meeting in Washington, D.C., on Tuesday.With more and more people moving out of the country and into cities each year, megacity air pollution is an emerging environmental and health problem, says Charles Kolb. 

https://www.sciencedirect.com/science/article/pii/S1352231007007911 

Due to its rapidly expanding economic and industrial developments, China is currently considered to be the engine of the world's economic growth. China's economic growth has been accompanied by an expansion of the urban area population and the emergence of a number of mega cities since the 1990. 

http://www.air-quality.org.uk/11.php 

The worst pollutant affecting the megacities as a whole is suspended particulate matter (SPM), particularly amongst megacities in the continent of Asia. This is of particular concern as high levels of SPM are known to be related to increased mortality rates, and in many of the megacities in developing countries health care for acute cases is less proficient than in developed countries.