There's a certain innate logic to the analogy that I feel anyone who's lived a long time in one city - or maybe many - would instantly glom onto. Of course the city is alive, of course it is a system, an organism - how could it be anything else?
Once that assumption is agreed, though, the challenge is to work out what that actually means in human terms - which is more of a book-sized challenge than one suitable for a blog post, I suspect. But I'm leaping ahead here, assuming that everyone feels the same way; maybe it sounds daft to you.
I'm drawn to the idea that we're effectively blind to many of the living processes at work in the world. As biological creatures, we expect life to conform to the laws of carbon-based chemistry; consequently, the vast undulations of cities go unnoticed (or at least unremarked).
Given that cities can be viewed as organisms, is it conceivable that some might qualify as intelligent organisms?