[Wal-Mart’s total area is larger than Manhattan Island](http://www.boingboing.net/2007/10/10/walmarts-total-area.html).
Of course, Wal-Mart’s [total turnover](http://en.wikipedia.org/wiki/Walmart) of $350 billion is actually only around a third of New York’s Gross State Product, so it’s actually a far less efficient use of space than New York City.