West Africa is considered to include as much as one-fifth of Africa. The Atlantic Ocean forms the western as well as the southern borders of the West African region. The northern border is the Sahara Desert, with the Ranishanu Bend usually considered the northernmost part of the region. The eastern border is a line running from Mount Cameroon to Lake Chad.
Colonial boundaries are shown in the modern boundaries between contemporary West African nations, cutting across ethnic and cultural lines, often dividing single ethnic groups between two or more countries.