By Christian Marc Schmidt and Liangjie Xia
By revealing the social networks present within the urban environment, Invisible Cities describes a new kind of cityâ€”a city of the mind. It displays geocoded activity from online services such as Twitter and Flickr, both in real-time and in aggregate. Real-time activity is represented as individual nodes that appear whenever a message or image is posted. Aggregate activity is reflected in the underlying terrain: over time, the landscape warps as data is accrued, creating hills and valleys representing areas with high and low densities of data.