The first thing that strikes visitors to China is the extraordinary density of its population. In the Han Chinese heartlands of central and eastern China, towns and cities seem to sprawl endlessly into one another in a world of chopsticks, tea, slippers, grey skies, shadow-boxing, teeming crowds, chaotic train stations, smoky temples, red flags and the smells of soot and frying tofu. Move west or north, however, and the landscape begins to dominate: green paddy fields and misty hilltops in the south-west, the scorched, epic vistas of the old Silk Road in the north-west; home to scores of distinct ethnic…