This is a report that Annie Myers completed last year, but it will stay relevant. It can be found on her blog, Thoughts on the Table.
"Over the last two months, I have conducted a research project focused upon urban farms and city planning, for the course City Planning 252 ("Land Use Controls"), taught by Professor Fred Etzel at UC Berkeley... you can download a full PDF file of the current report by clicking here... Your attention and feedback is appreciated!"