The Niger River and its tributaries (including the Benue, Kaduna, and Kebbi rivers) drain most of the country. Nigeria has a 500-mile (800-km) coastline, for the most part made up of sandy beaches, behind which lies a belt of mangrove swamps and lagoons that averages 10 mi (16 km) in width but increases to c.60 mi (100 km) wide in the great Niger delta in the east. North of the coastal lowlands is a broad hilly region, with rain forest in the south and savanna in the north. Behind the hills is the great plateau of Nigeria (average elevation 2,000 ft/610 m), a region of plains covered largely with savanna but merging into scrubland in the north. Greater altitudes are attained on the Bauchi and Jos plateaus in the center and in the Adamawa Massif (which continues into Cameroon) in the east, where Nigeria's highest point (c.6,700 ft/2,040 m) is located.
In addition to Abuja and Lagos, other major cities include Aba, Abeokuta, Ado, Benin, Enugu, Ibadan, Ife, Ilesha, Ilorin, Iwo, Kaduna, Kano, Maiduguri, Mushin, Ogbomosho, Onitsha, Oshogbo, Port Harcourt, and Zaria.
Nigeria is easily the most populous nation in Africa and one of the fastest growing on earth. The inhabitants are divided into about 250 ethnic groups. The largest of these groups are the Hausa and Fulani in the north, the Yoruba in the southwest, and the Igbo in the southeast. Other peoples include the Kanuri, Nupe, and Tiv of the north, the Edo of the south, and the Ibibio-Efik and Ijaw of the southeast. English is the official language, and each ethnic group speaks its own language. About half of the population, living mostly in the north, are Muslim; another 40%, living almost exclusively in the south, are Christian; the rest follow traditional beliefs. Religious and ethnic tensions have at times led to deadly violence in which hundreds of Nigerians have died.