Istanbul (Turkish: İstanbul) is the largest city in Turkey, constituting the country's economic, cultural, and historical heart. With a population of 13.9 million, the city forms one of the largest urban agglomerations in Europe[d] and is the third-largest city in the world by population within city limits.[2][3] Istanbul's vast area of 5,343 square kilometers (2,063 sq mi) is coterminous with Istanbul Province, of which the city is the administrative capital.[c] Istanbul is a transcontinental city, straddling the Bosphorus—one of the world's busiest waterways—in northwestern Turkey, between the Sea of Marmara and the Black Sea. Its commercial and historical center lies in Europe, while a third of its population lives in Asia.