Global Cities, an exhibition at the Tate Modern in London until August 27, “looks at the changing faces of ten dynamic international cities: Cairo, Istanbul, Johannesburg, London, Los Angeles, Mexico City, Mumbai, São Paulo, Shanghai and Tokyo.” Ogle Earth’s Stefan Geens visited the exhibition earlier today; he writes that it’s “a social geographer’s dream and a wonderful place for toddlers to explore. It’s a bit like Google Earth unplugged: population density maps you can climb, and big glorious imagery of cityscapes on the walls.” The photo above, of one of those climbable density maps, is by Stefan, and comes from his Flickr photoset of the visit.