Europe is traditionally defined as one of seven continents. Physiographically, it is the northwestern peninsula of the larger landmass known as Eurasia (or the larger Afro-Eurasia); Asia occupies the centre and east of this continuous landmass. Europe's eastern frontier is usually delineated by the Ural Mountains in Russia, which is the largest country by land area in the continent. The southeast boundary with Asia is not universally defined, but the modern definition is generally the Ural River or, less commonly, the Emba River. The boundary continues to the Caspian Sea, the crest of the Caucasus Mountains (or, less commonly, the river Kura in the Caucasus), and on to the Black Sea. The Bosporus, the Sea of Marmara, and the Dardanelles conclude the Asian boundary. The Mediterranean Sea to the south separates Europe from Africa. The western boundary is the Atlantic Ocean. Iceland is usually included in Europe because it is over twice as close to mainland Europe as mainland North America. There is ongoing debate on where the geographical centre of Europe falls. Overview Some geographical texts refer to a Eurasian continent given that Europe is not surrounded by sea and its southeastern border has always been variously defined for centuries. In terms of shape, Europe is a collection of connected peninsulas and nearby islands. The two largest peninsulas are mainland Europe and Scandinavia to the north, divided from each other by the Baltic Sea. Three smaller peninsulas—Iberia, Italy, and the Balkans—emerge from the southern margin of the mainland. The Balkan peninsula is separated from Asia by the Black and Aegean Seas. Italy is separated from the Balkans by the Adriatic Sea, and from Iberia by the Mediterranean Sea, which also separates Europe from Africa. Eastward, mainland Europe widens much like the mouth of a funnel, until the boundary with Asia is reached at the Ural Mountains and Ural River, the Caspian Sea, and the Caucasus Mountains. Land relief in Europe shows great variation within relatively small areas. The southern regions are mountainous while moving north the terrain descends from the high Alps, Pyrenees, and Carpathians, through hilly uplands, into broad, low northern plains, which are vast in the east. An arc of uplands also exists along the northwestern seaboard, beginning in southwestern Ireland, continuing across through western and northern Great Britain, and up along the mountainous, fjord-cut spine of Norway. This description is simplified. Sub-regions such as Iberia and