Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean. French people often refer to Metropolitan France as L’Hexagone (The “Hexagon”) because of the geometric shape of its territory. France is a unitary semi-presidential republic. Its main ideals are expressed in the Declaration of the Rights of Man and of the Citizen. France is bordered by Belgium, Luxembourg, Germany, Switzerland, Italy, Monaco, Andorra, and Spain. Due to its overseas departments, France also shares land borders with Brazil and Suriname (bordering French Guiana) , and the Netherlands Antilles (bordering Saint-Martin). France is also linked to the United Kingdom by the Channel Tunnel, which passes underneath the English Channel.