A city's built environment and people form its identity. Mark Twain said Memphis "is a beautiful city, nobly situated on a commanding bluff overlooking the river."     Redevelopment of Memphis city center includes culture, commerce, leisure and entertainment, and is driven partly by the migration of residents returning to the original urban center. Successful development is occurring through the preservation of and creative reuse of office buildings as apartments and hotels, and in warehouses as restaurants and offices.     Memphis residents are living in redeveloped buildings, attending events in restored theaters, and dining in restaurants converted from former industrial buildings.