A new study which examines 19 cities of 20 million people each (and in the 21st century) is about to be undertaken. This study, called 19.20.21, appears to be quite intriguing and I look forward to its results. Check out the site for some interesting urban facts, both historical and recent.
One question though: anyone know who is sponsoring the study? If you have any information about it, please contact me, or put the info into the comments.