Nigeria has borders with Niger to the north, Chad (across Lake Chad) to the northeast, Cameroon to the east and Benin to the west. To the south, the Gulf of Guinea is indented by the Bight of Benin and the Bight of Biafra. The country's topography and vegetation vary considerably. The coastal region is a low-lying area of lagoons, sandy beaches and mangrove swamps, which merges into an area of rainforest where palm trees grow to over 30m (100ft). From here, the landscape changes to savannah and open woodland, rising to the Central Jos Plateau at 1,800m (6,000ft). The northern part of the country is desert and semi-desert, marking the southern extent of the Sahara.