The terrain in the south is wooded savanna; it becomes brush country near Lake Chad. The only important rivers are the Chari and the Logone, both of which flow into Lake Chad and are used for irrigation and seasonal navigation. Northern Chad is part of the Sahara Desert; areas of the mountainous Tibesti region there are 11,000 ft (3,353 m) high. The country has no railroads and few all-weather roads.
Chad comprises some 200 ethnicities, which fall into two distinct, and often hostile, population groupings. In the south, where the bulk of the population is concentrated, live sedentary agricultural peoples, including the Sara, Massa, Ngambaye, and Moundang; most are Christians, but some follow traditional religions. In the north are seminomadic and nomadic Muslim peoples, including Arabs, Tuareg, Hadjerai, Fulbe, and Toubou. French and Arabic are the official languages, but more than 100 languages and dialects are spoken throughout the country.