@inbook{NBERc7980,
 Crossref = "NBERglae08-1",
 title = "Cities as Six-by-Six-Mile Squares: Zipf’s Law?",
 author = "Thomas J. Holmes and Sanghoon Lee",
 BookTitle = "Agglomeration Economics",
 Publisher = "University of Chicago Press",
 pages = "105-131",
 year = "2010",
 month = "February",
 URL = "http://www.nber.org/chapters/c7980",
}
@book{NBERglae08-1,
 title = "Agglomeration Economics",
 author = "Edward L. Glaeser",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "2010",
 URL = "http://www.nber.org/books/glae08-1",
}