Several hundred thousand square miles of the Great Plains have fewer than 6 inhabitants per square mile (2.3 inhabitants per square kilometer)—the density standard Frederick Jackson Turner used to declare the American frontier "closed" in 1893.
Nekoliko stotina tisuća četvornih kilometara Velike nizine imaju oko 3 osobe na četvrom kilometru—standard gustoće koji je Frederick Jackson Turner koristio da 1893. proglasi American Frontier "zatvorenim".