The Sahara Desert covers 3.6 million square miles in North Africa, bordered by the Red Sea in the east, the Mediterranean Sea to the north, the Atlantic Ocean in the west and the Sahel savannas to the south. It's the world's largest hot desert and blankets 10 percent of Africa.
The Sahara Desert stretches through 10 countries. Its geography and climate vary from one area to another. The central Sahara is in a climatic divide, a boundary causing different climates to form on each side. Near the Mediterranean coast and the Sahel savannas, it receives more rainfall than toward its center, creating a hyper-arid climate. Sand seas called ergs with massive dunes make up 25 percent of the desert, while the rest is rocky plateaus, mountains, salt flats, plains and valleys. The Nile is the only permanent water source in the Sahara.