The Pulse of a City

What's interesting about a large city is you see some strange phenomena. For example, I live in London and if you wander around what you will notice is people appear in discrete groups (or pulses or quanta). These quanta are dictated by the frequency of the public transport system. The phenomena is more apparent close to a train station and during rush hour, or along a busy shopping street (such as Oxford Street). Perhaps one could say that the public transport dictates the pulse of the city.