Sierra Leone (/sɪˈɛərə lɪˈoʊni, -lɪˈoʊn/), officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea in the north-east, Liberia in the south-east, and the Atlantic Ocean in the south-west. Sierra Leone has a tropical climate, with a diverse environment ranging from savannah to rainforests. Sierra Leone has a total area of 71,740 km² (27,699 sq mi) and an estimated population of 6 million (2011 United Nations estimate). Freetown is the capital, largest city, and its economic and political centre. Bo is the second largest city and second major economic center in the country.