I caught the end of a very interesting conversation at Harvard on the politics of urban space and I was reminded of my most basic definition of politics: politics is the means by which we allocate power. What is power? Power is who gets to determine what, or slightly more expressively whose priorities determine our public choices. Priorities are ultimately expressions of values. So politics is the vehicle by which we determine whose values hold sway. Democratic politics allows for transitions for one set of values to other sets of values peacefully, either quickly or over time, through elections and political action.
What is interesting about urban space is that it is "sticky" - to use the term often used by economics to describe wages - its capacity to incorporate change is much slower than that of politics. Once built, it takes a building, a street, a tunnel, a bridge, a very long time to get unbuilt. Not that things don't get unbuilt - just think of Paris in the 1860s, when Haussmann destroyed a 600 year old city to build a new one in its place, or less dramatically think of Pennsylvania Station in New York City, one of the great architectural gems of the first years of the 20th century, unbuilt in 1960s at the hands of a changing urban dynamic, different tastes, and a new power structure.
It also bears remembering that urban space is always a representation of power (I think of Versailles, the quintessential demonstration of power through built form), and at the same time a conferrer of power (the Mall is Washington is an excellent example of this). We err if we imagine that urban spaces can somehow be separated from the people who create them and who use them.