The 2011 Revision presents estimates and projections of the total, urban and rural populations of the world for the period 1950-2050. The results are shown for development groups, six major areas (i.e., Africa, Asia, Europe, Latin America and the Caribbean, Northern America and Oceania) and 21 regions. Data are further presented for the 231 countries or areas of the world. The 2011 Revision also provides estimates and projections of the population of urban agglomerations with at least 750,000 inhabitants in 2011 for the period 1950-2025. Estimates of the proportion of the population living in urban areas and the population of cities are based on national statistics. Population censuses are the most commonly used sources of data on the proportion urban and the population of cities. However, in some countries, the data used as the basis for estimation are obtained from population registers or administrative statistics.