NEW DELHI: At present, India is home to five mega ci ties, with over 10 million population, but by 2030 this number will go up to seven. Delhi will continue to be the second most populous city in the world till 2030, adding a staggering 9.6 million people to its population ­­the most in any mega city .The facts have been revealed in the 2016 World Cities Report issued by the UN's department of economic and social affairs.The report has not relied on the administrative boundaries of cities but has, instead, preferred to use the concept of "urban agglomeration" which is the "the contiguous urban area, or builtup area". For example, in the case of Delhi urban agglomeration, the satellite cities of Ghaziabad, Noida, Faridabad and Gurgaon are included. Such inclusion makes sense as people in these contiguous areas are economically and socially integrated with the main city .Around the world, about 500 million people live in 31 such mega cities. That's about 6.8% of the world's population or 12% of the world's urban population.The report calculates that by 2030, the number of mega cities will increase to 41 and their population to about 730 million or 8.7% of the world's population. Other Indian cities figure in 2016's mega cities listing in 2016's mega cities list are Mumbai, Kolkata, Bengaluru and Chennai. By 2030, Hyderabad and Ahmedabad will join them, as their respective populations would cross 10 million.The UN report shows that only a minority of urban dwellers actually live in mega cities. Nearly 21% of the world's population stays in cities of population between 500,000 to 10 million, while an even bigger share of 26.8% resides in smaller cities and towns with a population of less than 500,000.By 2030, the world's population will decisively shift to urban living with 60% of the estimated population living in cities, big or small. Currently, about 54% of the world's population is urban.Most of the urban growth is happening in developing countries in Asia and Africa. By 2030, as many as 33 of the 41 mega cities will be from the third world.Of the 47 cities that grew by over 6% every year be tween 2000 and 2016, six were in Africa, 40 in Asia (including 20 in China) and just one in North America.Interestingly , not all cities are growing. Out of the 1,063 cities with a population over 500,000, as many as 55 have shown a decline since 2000. Most of these cities are located in Europe and some in Japan. Their decline is mostly due to falling fertility levels, although some have shown a dip in population due to natural calamities like New Orleans (due to hurricane Katrina) and Sendai in Japan (tsunami).