Sudan occupies 2 500 000 km in East Africa. It has borders with nine countries, two of which are Arab: Egypt, Libya, Kenya, Uganda, Congo, Chad, the Central African Republic, Ethiopia and Eritrea. Sudan is the largest country in Africa. The heart of the country, in terms of population, lies at the confluence of the Blue and White Niles. The complex of the 'three towns', comprising the three largest cities, Khartoum, Khartoum North and Omdurman, is situated there and contains almost 20% of the population. The total population of Sudan is about 35.4 million (projected from the 2005 census). The urban population was estimated at 33% of the total. About 2.2 million are still entirely nomadic. Sudan's peoples are as diverse as its geography. There are 19 major ethnic groups and 597 subgroups.