The urban population is estimated to be 11 percent of the total population. The rural lowland population is composed of many nomadic and seminomadic peoples. The nomadic peoples seasonally graze livestock, while the seminomadic peoples are subsistence farmers. The rural highlands economy is based on agriculture and livestock raising.
The central plateau, known as the highlands, is surrounded on three sides by desert with a significantly lower elevation. The plateau is between six thousand and ten thousand feet above sea level, with the highest peak being Ras Deshan, the fourth-tallest mountain in Africa. Addis Ababa is the third-highest capital city in the world.
The Great Rift Valley (known for discoveries of early hominids such as Lucy, whose bones reside in the Ethiopian National Museum) bisects the central plateau. The valley extends southwest through the country and includes the Danakil Depression, a desert containing the lowest dry point on the earth. In the highlands is Lake Tana, the source of the Blue Nile, which supplies the great majority of water to the Nile River Valley in Egypt.
