The stack flow above by Barcelona design concern Bestiario depicts the 590 most populated cities sorted column by their population between 1950 and 2010 in 5 year intervals, and projected for 2015, 2020, 2025. Cities’s colors are generated from their geographic coordinates, with the hue varying with longitude, as the below image shows (cirlces areas are proportional to cities population in 2010). The interactive version is quite a data dump – I wish you could isolate just one city and turn off the rest.