Cities are such interesting places, and quite a strange idea if thought about objectively. They contain the stories and hopes and troubles of millions upon millions of people. The lives of people are so intermingled in cities- any one person's actions, whether as subtle as smiling at a stranger, or as significant as causing a car crash, could easily affect the lives of many other people.
And yet, it is a rare occurrence that people in cities acknowledge each other. We see through other spiritually absent citizens of our homes like they are made of air and often ignore the ones who are present and acknowledge us.
The idea of a city, the concept, is truly one that could only have been thought of by human beings.