Europe is traditionally reckoned as one of seven continents. Physiographically, however, it is the northwestern peninsula of the larger landmass known as Eurasia (or Afro-Eurasia): Asia occupies the eastern bulk of this continuous landmass (save the Suez Canal separating Asia and Africa) and all share a common continental shelf. Europe’s eastern frontier is delineated by the Ural Mountains in Russia. The south-east boundary with Asia is not universally defined. Most commonly the Ural or, alternatively, the Emba River serve as possible boundaries. The boundary continues to the Caspian Sea, the crest of the Caucasus Mountains or, alternatively, the Kura River 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, though on the Mid-Atlantic Ridge and nearer to Greenland (North America) than mainland Europe, is generally included in Europe for cultural reasons. There is ongoing debate on where the geographical centre of Europe is.
The idea of a European “continent” is prevalent but not universally held. Some geographical texts refer to a Eurasian Continent, or to a European subcontinent, given that Europe is not surrounded by sea and its Southeastern border has always been vaguely defined, and disputed.
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 (or, less commonly, the Este River), the Caspian Sea and 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 the western British Isles and continuing along the mountainous, fjord-cut spine of Norway.
This description is simplified. Sub-regions such as Iberia and Italy contain their own complex features, as does mainland Europe itself, where the relief contains many plateaus, river valleys and basins that complicate the general trend. Iceland and the British Isles are special cases. The former is a land unto itself in the northern ocean which is counted as part of Europe, while the latter are upland areas that were once joined to the mainland until rising sea levels cut them off.