The garden as a metaphor for the city

Flying into Toronto the other day, I got a chance to look down at the buildings surrounding the airport. It struck me how many houses there were, and how few taller buildings. I then started thinking that cities could be viewed like gardens. Houses and other low-lying structures are ground cover. Basic tract houses remind me of grass. They look very homogeneous from the air. Taller buildings are plants. They stand out above the ground cover, but with the way architecture has been unremarkable in the past century, very few of these plants can be called flowers. We seem, also, to be missing shrubs. I don't think we have the buildings yet that could be likened to shrubs.

So, how can we make our cities into better gardens? More flowers. That means more variety, more colour, and taking more chances with architecture. Some different varieties of ground cover might be nice, too. And shrubs: I'd like to figure out what architectural shrubs could be.