Wal-Mart stores are often the size of four or five football fields - huge in scale compared to many of the small communities that they neighbor. Criticized for deserting stores that under-perform, Wal-Mart has left behind more than 25 million square feet of unoccupied space across the country

And they also have this quote:

People are surprised that Wal-Mart would even want to locate a store at Ashland, with another one 10 miles away. But that's part of the Wal-Mart saturation strategy. They place their stores so close together that they become their own competition. Once everybody else is wiped out, then they're free to thin out their stores. Wal-Mart has 390 empty stores on the market today. This is a company that has changed stores as casually as you and I change shoes.