This article in Forbes Magazine describes the creation of a data visualization called Tube Heartbeat. Produced by Oliver O’Brien it shows the movement of London England’s transit passengers as they move around the 268 tube stations on 11 lines. The images are updated in fifteen minute intervals, showing how up to 4.8 million passengers a day use the system.

We already use analogies like arterials for the road network-the pulsing of the volume of passengers using the London tube  network  looks very organic, confirming that public transportation is indeed the heart of a city.