] Despite almost four millennia as centres of civilisation,
] it was only fairly recently that cities attracted more
] than a small percentage of the global population. With
] hindsight, the 20th Century was the century of
] urbanisation.
]
] In 1900, only 14% of humanity lived in cities. By the
] century's close, 47% of us did so. This change is
] revealed in the growth of the number of medium-sized
] cities. In 1950, there were 83 cities with populations
] exceeding one million; but by 2000, this had risen to
] 411.

Of course, at least in the US, some of this may be attributed to an increased definition of 'urban' space. The city lines of a city founded in 1950 is far more generous than 1850 or 1750.