The terrain is covered mainly by dense tropical rain forest, with stretches of wooded savanna. Tributaries of the Congo and Ubangi rivers, which separate Congo from the Democratic Republic of the Congo, flow through the country. The climate is warm and humid and rainfall is heavy. The Congo serves as the transport and commercial hub of central Africa, with economically important road, river, and rail systems connecting inland areas with the Atlantic. The country's internal road network is inadequate, however, and has hampered economic development.
About half of the nation's population resides in urban areas, and the population density is relatively low. There are about 15 ethnic groups in Congo, and these are subdivided into some 75 smaller groups. The Bakongo, who make up nearly half of the population, are mostly farmers or traders and live primarily around Brazzaville; they are Bantu-speaking, as are the Bateke (who live north of Brazzaville), the Sanga, and the Mbochi. Pygmies live in the north, and Vili people dwell along the coast. About half of the Congolese people practice traditional religions; the rest are primarily Christian, although there is a small Muslim minority. French is the country's official language, but many African languages, including Lingala and Monokutuba (both lingua franca trade languages) and Kikongo, are widely spoken.