Nigeria, officially named the Federal Republic of Nigeria, is a federal constitutional republic comprising thirty-six states and one Federal Capital Territory. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in the north. Its coast lies on the Gulf of Guinea, part of the Atlantic Ocean, in the south. The capital city is Abuja. The people of Nigeria have an extensive history, and archaeological evidence shows that human habitation of the area dates back to at least 9000 BC. The Benue-Cross River area is thought to be the original homeland of the Bantu migrants who spread across most of central and southern Africa in waves between the 1st millennium BC and the 2nd millennium AD. Nigeria is the most populous country in Africa and the eighth most populous country in the world with a population of over 140 million. It is a regional power and it is also listed among the "Next Eleven" economies. The economy of Nigeria is one of the fastest growing in the world with the International Monetary Fund projecting a growth of 9% in 2008 and 8.3% in 2009. Nigeria is located in western Africa on the Gulf of Guinea and has a total area of 923,768 km² (356,669 mi²),[33] making it the world's 32nd-largest country (after Tanzania). It is comparable in size to Venezuela, and is about twice the size of California. It shares a 4047 km (2515-mile) border with Benin (773 km), Niger (1497 km), Chad (87 km), Cameroon (1690 km), and has a coastline of at least 853 km.[34] The highest point in Nigeria is Chappal Waddi at 2,419 m (7,936 feet). Nigeria has a varied landscape. From the Obudu Hills in the southeast through the beaches in the south, the rainforest, the Lagos estuary and savannah in the middle and southwest of the country and the Sahel to the encroaching Sahara in the extreme north.