Istanbul is the largest city in Turkey, serving as the nation's primary economic, cultural, and historical center. It is one of the most populous cities in both Europe and the world, housing over 15 million people, which accounts for approximately 18% of Turkey's total population.
The city is uniquely situated on two continents, with roughly two-thirds of its residents living in Europe and the remainder in Asia. It straddles the Bosphorus, one of the world's busiest waterways, located in northwestern Turkey between the Sea of Marmara and the Black Sea. The city's total area covers 5,461 square kilometers (2,109 mi2) and is coterminous with Istanbul Province.