Cuba is an island nation in the Caribbean Sea. Cuba has a total land area of 110,860 km² (42,803.3 sq mi). It has 3,735 km (2,321 mi) of coastline and 29 km (18 mi) of land borders — all figures including the United States territory at Guantánamo Bay, where the U.S. Navy's Guantanamo Bay Naval Base is located. Cuba lies west of the North Atlantic Ocean, east of the Gulf of Mexico, south of the Straits of Florida, northwest of the Windward Passage, and northeast of the Yucatan Channel. The main island (Cuba) makes up most of the land area 105,006 km² (40,543 sq mi). The island is 1,199 km (745 mi) long and 200 km (124 mi) across its widest points and 35 km (22 mi) across its narrowest points. The largest island outside the main island is the Isla de la Juventud (Isle of Youth) in the southwest, with an area of 3,056 km² (1,179.9 sq mi). At 587,041 km² (226,657.8 sq mi), Madagascar is the world's 46th-largest country and the fourth largest island. It is slightly larger than France and it also is one of 11 distinct physiographic provinces of the South African Platform physiographic division. Towards the east, a steep escarpment leads from the central highlands down into a ribbon of rain forest with a narrow coastal further east. The Canal des Pangalanes is a chain of natural and man-made lakes connected by canals that runs parallel to the east coast for some 460 km (about two-thirds of the island). The descent from the central highlands toward the west is more gradual, with remnants of deciduous forest and savanna-like plains (which in the south and southwest, are quite dry and host spiny desert and baobabs). On the west coast are many protected harbours, but silting is a major problem caused by sediment from the high levels of erosion inland.