Mumbai and Delhi would become among the most populous cities in the world by 2020, with both expected to touch nearly 24 million and the former having more people packed in a single square kilometre than any other city.
The year 2007 marks the first time in the history of mankind when more than half the world's population lives in cities. And India's 300 million city dwellers add up to one-tenth of the world's urban population.
These figures were released prior to an Urban Age India conference that opens in India's commercial capital Mumbai on Nov 1.
Urban Age aims to "shape the thinking and practice of city leaders and sustainable urban development". It was initiated by the London School of Economics (LSE) and Deutsche Bank's Alfred Herrhausen Society, and has studied and visited Indian metropolitan cities as well as New York, Shanghai, London, Mexico City, Johannesburg and Berlin.
The study found that Greater Mumbai has a density of 27,348 people packed in each square kilometre, as against Kolkata's 24,454, Bangalore's 19,040 and Delhi's 9,340.
In its 'peak density' area, Mumbai has as many as 101,066 people packed in a single square kilometre - more than any other of the nine cities globally included in this study.
Yet, home to 12 million inhabitants in an area half the size of Berlin, less than half of Greater Mumbai is covered by built-up land and infrastructure. A national park and open areas, coastal wetlands, mangroves, agricultural land and even beaches occupy large areas.
Population growth in India's urban areas has been dramatic too. Between 1950, 2007 and 2020 (projected), Mumbai has grown from 2.8 million to 18.9 million and will touch 23.9 million. Some believe it could cross Tokyo as the most populated city globally.
In the same time frame, Delhi has spurted from 1.4 million to 16.6 million to reach 23.7 million and Kolkata from 4.5 million to 14.8 million and 18.7 million. Bangalore's growth moved from .7 million to 6.9 million at present and is estimated to touch 9.5 million by 2020.
Going by these projections, Mumbai and Delhi would be among the most populous in the world by 2020, followed by Mexico City (22.1 million), New York (20.3 million), Kolkata (18.7 million), and Shanghai (18.4 million).
Besides Greater Mumbai's extremely high population density, the city also faces issues of traffic congestion, loss of wetlands, flooding and critical housing issues.
Delhi's problems are seen as rapid population growth and large unplanned urbanisation. Besides, there's stretched-out infrastructure, unaffordable housing and growing slums, traffic congestion and "significant ecological degradation".
Kolkata's woes include the loss of city wetlands, causing frequent flooding, traffic congestion, inadequate infrastructure and pollution.
Bangalore, meanwhile, hurts from rapid urbanisation, pollution, waste disposal and sewerage and sanitation problems, loss of its tree cover, and high traffic congestion.
When it comes to moving in the city, some 55.5 percent Mumbaites walk, 21.9 percent go by train, 14.4 percent opt for the bus, and only 1.6 percent take their car. Rickshaw and taxi, two-wheelers and cycles are used by only a small number of people.
Mumbai has the lowest level of car ownership with 29 cars per 1,000 residents, a stark contrast to Mexico City's 383.
Kolkata and Bangalore have the highest number of cars per kilometre among Indian cities. With 1,421 cars per kilometre, Kolkata's car density is even higher than that of Berlin.
Someone living in Mumbai has a life expectancy of 68.1 years as against 79.2 years in London or 75.9 years in Mexico City. On the positive side, Indian cities have relatively low murder rates, similar to London and Shanghai.
But some other problems are more severe. For instance, although "precarious urbanisation" affects many countries, the extent of slums in India "makes its cities unparalleled sites to reflect on strategies to better accommodate the growing number of urban residents and their multiple needs".
"India's status as a developing nation with a growing urban economy, coupled with the sheer magnitude of people and social potential, provide an ideal platform for the analysis and discussion of the future shape of urban society," argue LSE's Urban Age director Ricky Burdett and Alfred Herrhausen Society managing director Wolfgang Nowak in a statement made in the run-up to the event.