Nigeria, officially the Federal Republic of Nigeria, is a country in West Africa. It is the most populous country in Africa; geographically situated between the Sahel to the north, and the Gulf of Guinea to the south in the Atlantic Ocean; covering an area of 923,769 square kilometres (356,669 sq mi), with a population of over 211 million. Nigeria borders Niger in the north, Chad in the northeast, Cameroon in the east, and Benin in the west. Nigeria is a federal republic comprising 36 states and the Federal Capital Territory, where the capital, Abuja, is located. The largest city in Nigeria is Lagos, one of the largest metropolitan areas in the world and the second-largest in Africa