Istanbul, Turkey
Here’s trouble: Istanbul (population 10 million) sits on the site of a vicious fault line that has coughed up lethal earthquakes. The most recent, in 1999, caused massive loss of life as a result of a densely packed population and the fact that large swathes of housing development — built in haste to accommodate the city’s rapid growth — were flimsy constructions. Geologists predict another major disaster some time within the next few decades, throwing into sharp relief the need for megacities to somehow grow megabrains and do some serious thinking about the consequences of rampant development.

Mexico City, Mexico
Chiming in with 22 million people, Mexico City can’t help but represent both poles of the megacity experience. Let’s get the bad out of the way: the pollution here is extraordinary, a brown shell hanging over the city like a geodesic dome from hell. Then there’s the suffocating poverty, the corruption, the slums, the alarming crime rate. But then again, there’s the justly famous museums, the vibrant music, the zesty arts scene, the remarkably well preserved sense of history. In short, this is one hell of a complex megacity.

Mumbai, India
Mumbai (population 17 million) means Bollywood; endless shopping malls; unbelievable pollution; crass commercialism; cricket and more cricket; food, food and more food; chai; writhing, snarling, totally unpredictable traffic jams; buzzy street scenes; intoxicating nightlife; humidity like a hammer; grinding slums; beggars; luxurious spas; sacred cows; Kingfisher beer; the Ganesh Festival and a few million revellers out on the streets at once; incubator of dreams for countless Indians…

Seoul, South Korea
Repeatedly flattened by conflict (the Japanese and Manchu attacks of the 16th and 17th centuries and the Korean War more recently), Seoul (population 23 million) has bounced back to become a shrine to modern life, with high-rises, big business and freeways galore. But now it’s greening up, planting over three million trees since 1998, developing the US$200 million Seoul Forest, and reinvigorating its public-transport system to wean residents off their car addiction. Given the 21st-century forecast of more and more megacities worldwide, Seoul is far and away the exemplar in how to give a damn.

Karachi, Pakistan
Although the port city of Karachi (population 15 million) has become increasingly affluent and urbanised, it has suffered from frequent outbreaks of cholera, emphasising the way in which megacities magnify pain alongside pleasure. Still, Karachi is Pakistan’s cultural centre, a city with a rich sense of history and a multiethnic community. It’s rapidly becoming an Asian tourism hot spot, with the markets, bazaars and cricket the major drawcards, as well as the nearby beaches.

Tokyo, Japan
Tokyo, inspiration for dystopian science-fiction flick 'Blade Runner', was once described by William Gibson as ‘the global imagination’s default setting for the future’; Greater Tokyo, the world’s biggest megacity (population 35 million), has swallowed up nearby cities including Yokohama and Kawasaki. It’s a beast of a place, a living, breathing organism constantly reinventing itself and generating hyper accelerated fashion, design, technological prowess...plus attendant health problems, pollution, traffic-driven nightmares. Track its transition from the diminutive 'Tokyo' to the untameable 'Greater Tokyo' and you are in fact tracking Japan’s speed-of-light rise — and subsequent decline — as an economic superpower.

Moscow, Russia
If you like your megacities cold, then don't pass up Moscow (population 11 million) — the average temperature here is just 5°C, meaning three times more energy is needed to heat the place than your average Asian megacity. And that means a terrible time for the environment. Here's hoping the Russian government can get cracking and cook up some sustainable solutions, but in the meantime you all know what Moscow’s good for: history, culture all the basic essentials.

Bangkok, Thailand
It may be a megacity — huge (population 12 million), modern, increasingly Westernised — but Bangkok still retains a somnambulant village air… albeit one that’s continually disrupted by the ever-present thrum of mega-traffic and mega-nightlife. Still, Bangkok, unlike Mexico City and Mumbai, has gone some way to controlling its pollution. But enough of that: Bangkok is also surprisingly historical. Before you know it, your nostrils will be twitching from incense rather than smog as you stumble upon a temple in the thick of it all.

New York, USA
OK, this is where it all began: New York was the first city to bust the 10-million-people barrier, somewhere in the late ’40s, kicking off the megacity trend that continues apace, worldwide, in the 21st century (today NY’s greater metropolitan area has doubled to 19 million people). There’s not that much to utter about Noo Yawk that hasn't been kicked to death by numerous go-rounds in Woody Allen (lite) and Martin Scorsese (dark) movies, suffice to say that there’s a lot of dog shit on NY pavements because there’s a hell of a lot of dogs.

Shanghai, China
Possibly the world’s fastest-growing megacity, Shanghai (population 18 million) was voted ‘most exciting city in the world’ by Time magazine, a far cry from its old rep as crucible of the sleaziest vice this side of Miami. Yes, it’s exciting if you like the smell of big finance. But scintillating Shanghai is also tops for sophisticated, big-city life including the best of art, cutting-edge architecture and fine cuisine. Then there are the crumbling remnants of Shanghai’s decadent colonial past, plus temples, gardens and bazaars. Megacity madness! Plus, it’s the Birth-place of author, JG Ballard, and for many that’s recommendation enough.