A defining trend for for the first half of the century: urbanization on steroids:
“Less than 5 per cent of the world’s population lived in cities a century ago. In 2008, for the first time in humanity, that figure exceeded 50 per cent. In the last two decades alone, the urban population of the developing world has grown by an average of 3 million people per week.”
“By 2050, it will have reached 70 per cent, representing 6.4 billion people. Most of this growth will be taking place in developing regions; Asia will host 63 percent of the global urban population, or 3.3 billion people in 2050.” (Source: the Global Report on Human Settlements 2009 )
Download the graphs and charts here: http://www.unhabitat.org/documents/GRHS09/mapsindd.pdf