Cities are 2% of the earth's crust, but they are 50% of the world's population.

Today, for the first time - and the Obama campaign showed us this - we can go from the digital world, from the self-organizing power of networks, to the physical one.

Like a tracer running through the veins of the city, networks of air quality sensors attached to bikes can help measure an individual's exposure to pollution and draw a dynamic map of the urban air on a human scale, as in the case of the Copenhagen Wheel developed by new startup Superpedestrian.

This raises some serious privacy issues. But where better than to work these concerns out but on a research campus?

Phone networks can capture life on our planet.

As people talk, text and browse, telecommunication networks are capturing urban flows in real time and crystallizing them as Google's traffic congestion maps.