Harvard has a PhD program in Visual and Environment Studies. I am not sure if they have faculties specifically working on the topic of urban spaces, but it is probably worth checking out. UC San Diego might be of your interest as well. Their communication program as well as digital arts program are both great places.
Since it is a pretty interdisciplinary field of interest, I would suggest looking at more flexible and multidisciplinary programs so that you have more opportunities to work with faculties across departments. UC Irvines, UC Santa Cruz, UC Santa Barbara, Northwestern, USC, and MIT might have programs that have faculties who specialize in media and urban space.