Humans are about to become a primarily urban species.
China is growing at breakneck speed
Sometime in the next couple of years there will be more people living in cities than in rural areas.
The pace of change over the last 50 years has swallowed up large tracts of countryside and transformed towns into cities, cities into megacities.
The BBC is running a special season of features, quizzes, picture galleries and statistical guides starting next week and we would like your help.
Have you any pictures showing the old and the new? We're interested in images that show the 'before and after' of urbanisation. Have you photographs of rural areas before the arrival of concrete? Send them to firstname.lastname@example.org.
Please put 'before and after' in the subject heading.