So, Istanbul. Decades after the Ottoman Empire said goodbye to its last Sultan in 1922 the population of Istanbul was what it had been at the end of the 19th century—hovering around a million. That’s not a lot for a city that big; it must have felt as empty as Baltimore does sometimes. Since then, Istanbul’s population has grown thirteen fold, and like its income, it’s still growing fast compared to metropolitan areas in other industrialized nations. How does this happen?