This interactive data visual illustrates the scale and speed of urban transformation that research by the International Institute of Environment and Development (IIED) has sought to document and describe. A guide to its use can be found underneath the visual.
The visitor can use a slided to advance through the years and to see how and where cities have grown since 1800, plus predictions for future growth until 2025. A written summary of the wider global changes taking place can be found at the top, while users who hover their mouse over individual cities can discover precise data regarding those cities.
For example in 1800 there were only three cities with populations above 750,000. By 1900 there were 25. This increased to 105 in 1950, 473 in 2000 and 611 in 2010. The map does not project the number after 2015.