West Africa is west of an imagined north-south axis lying close to 10° east longitude. The Atlantic Ocean forms the western and southern borders of the West African region. The northern border is the Sahara Desert, with the Ranishanu Bend generally considered the northernmost part of the region. The eastern border is less precise, with some placing it at the Benue Trough, and others on a line running from Mount Cameroon to Lake Chad.