In his Daily Dose of Architecture posting for May 25, 2010 (http://archidose.blogspot.com/2010/05/walhattan.html), John Hill included a graphic from Jesse LeCavalier's essay "All Those Numbers" at Places: Design Observer (http://places.designobserver.com/entry.html?entry=13598 .) The graphic compares the size of the floor area of Wal-Mart (and affiliated) stores to the area of Manhattan and is copied below.
While a dramatic graphic, the footprint of the stores is only part of the story. For a true comparison of the built area of Wal-Mart stores, you would need to include the parking lots. This would result in a Wal-Mart footprint that is four to five times larger than what is show above. It would look something like what is shown below.