@inbook{NBERc7980,
 Crossref = "NBERglae08-1",
 title = "Cities as Six-By-Six-Mile Squares: Zipf’s Law?",
 author = "Thomas J. Holmes and Sanghoon Lee",
 year = "2007",
 month = "December",
 URL = "http://www.nber.org/chapters/c7980",
}