The main geographical feature of the landlocked country is the White Nile and its tributaries, including the Bahr el Ghazal, the Yei, and the Sabat. The plains and hills in the northern and central parts of the country are characterized by swampland (the enormous Sudd, which constitutes one sixth of the country), savanna, and forests. The terrain rises to mountains in the extreme south; the highest point is Kinyeti (10,456 ft/3,187 m) on the border with Uganda. The tropical climate is marked by seasonal rainfall; the plains are drier than the southern highlands.
The largest ethnic groups in the ethnically diverse nation are the Dinka, Nuer, Shilluk, and Bari, all of whom speak Nilotic languages, and the Azande, who are Bantu speakers. Most South Sudanese follow traditional African religious beliefs, but about 18% are Christian and some are Muslim. English is the country's official working language, but Arabic is the lingua franca; all indigenous languages are constitutionally recognized as national languages.