In 2008, for the first time, the world’s urban population surpassed the rural
population, crossing the threshold of 50%, according to the most coherent and most
comparative estimates at international level (United Nations: Population Division,
2008). Indeed, the major obstacle to overcome in the study of the world urbanization
resides in differences in the definition of urban agglomerations and their limits among
various countries, as well as in the modification of these limits over time.
The situation varies sharply from region to region, both with regard to the urbanization
ratio (or proportion of urban population) and to the number of megalopolises [megacities]
(agglomerations of more than 10 million inhabitants). Estimated at 49.4%
worldwide in 2007, the urbanization ratio, in the large regions was as follows: North
America (81.3%), Latin America and the Caribbean (78.3%), Europe (72.2%), Oceania
(70.5%), Asia (40.8%), and Africa (38.7%). At the same time, there are 19 megalopolises
in the world: 11 in Asia, 4 in Latin America, 2 in North America, 1 in Africa and 1 in
Europe. Asia records a number of megalopolises deemed to expand the most.