France, officially the French Republic, is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean. It is often referred to as l’Hexagone ("The Hexagon") because of the geometric shape of its territory. It is bordered (clockwise starting from the northeast) by Belgium, Luxembourg, Germany, Switzerland, Italy and Monaco; with Spain and Andorra to the south. France is linked to the United Kingdom by the Channel Tunnel, which passes underneath the English Channel.