Christopher Alexander's The Pattern Language could help. And there is always Kevin Lynch, What Time Is This Place? The Image of the City. These all fit a public square into context in one way or another. Also, Michael Hough's Out of Place.
I've read Lynch's "Image of the City," and I thought it was a decent book. His analysis and application of the components of the cityscape was the strongpoint of the book. I wasn't too impressed with the rest of the book, including the LA/Jersey/Boston segment.