The Bosphorus or Bosporus, also known as the Istanbul Strait, is visible here as the thick black line separating the two land masses. It is the strait that forms the boundary between the European part of Turkey (Thrace) and its Asian part (Anatolia).
The world’s narrowest strait used for international navigation, it connects the Black Sea (top) with the Sea of Marmara (bottom). Upon opening the full image, many ships and their wake trails are visible north of the strait.
The Bosphorus is approximately 30 km long, with a maximum width of 3,700 metres at the northern entrance, and a minimum width of 700 metres between Kandilli and Aşiyan; and 750 metres between Anadoluhisarı and Rumelihisarı. The depth varies from 36 to 124 metres in midstream.
The shores of the strait are heavily populated as the city of Istanbul (with a metropolitan area in excess of 11 million inhabitants) straddles it. Based on the white areas in the image, it appears that the area towards the Sea of Marmara is more populated than that towards the Black Sea.