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SIZING UP CITIES "Chongqing has become the largest city not only in China but in the world", the media has proclaimed. More or Less casts doubt on both those claims. So which is the world's biggest city, and what is its population? Two simple questions that we discover are surprisingly difficult to answer. Luckily, geographers Professor Kam Wing Chan, of the University of Washington, and Rich Greene, of the University of Northern Illinois, are on hand to help out. WEIGHING THE WORLD Has the world got heavier or lighter since the industrial revolution? It's a question posed by a More or Less listener that got us wondering, too. Dr Chris Smith, part of a group of Cambridge University researchers, known as the Naked Scientists, reckons he's worked out the answer. Producer: Ruth Alexander (Image: Tokyo skyline at sunset. Credit: AFP/Getty Images)