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The boundaries between the continents of Earth are generally a matter of geographical convention. Several slightly different conventions are in use. The number of continents is most commonly considered seven but may range as low as four when the Americas and Afro-Eurasia are each considered a single continent. According to the definition of a continent in the strict sense, an island cannot be part of any continent, but by convention and in practice most major islands are associated with a continent. There are three overland boundaries subject to definition: *between Europe and Asia (dividing Eurasia): along the Turkish Straits, the Caucasus and the Urals (historically also north of the Caucasus, along the Kuma–Manych Depression or along the Don River) *between Asia and Africa (dividing Afro-Eurasia into Africa and Eurasia): at the Isthmus of Suez *between North America and South America (dividing the Americas): the Isthmus of Panama While the isthmus between Asia and Africa and that between the two Americas are today navigable, via the Suez and Panama canals, man-made diversions and canals are generally not accepted on their own accord as continent-defining boundaries; the Suez Canal happens to traverse the isthmus between the Mediterranean Sea and Red Sea, dividing Asia and Africa. The remaining boundaries concern the association of islands and archipelagos with specific continents, notably: *the delineation of Southeast Asia from Australasia *the delineation between Africa, Europe and Asia in the Mediterranean Sea *the delineation between Asia and Europe in the Arctic Ocean *the delineation between Europe and North America in the Atlantic Ocean *the delineation between North and South America in the Caribbean Sea *the delineation of Asia from North America in the North Pacific Ocean ==Europe and Africa== The European and African mainlands are non-contiguous, and the delineation between these continents is thus merely a question of which islands are to be associated with which continent. The Portuguese Atlantic island possession of the Azores is from Europe, from Africa, and is usually grouped with Europe if grouped with any continent. By contrast, the Canary and Madeira islands off the Atlantic coast of Morocco are much closer to and usually grouped with Africa (Madeira is from Europe and from Africa).〔http://spainforvisitors.com/sections/canaryislands.htm〕 The island nation of Malta is approximately from the coast of Sicily in Europe - much closer than the distance to the closest African coast. The nearby Italian island of Lampedusa is from Sicily while just from the African coast; similarly, Pantelleria is from Sicily and just from the African coast. All are generally included within Europe if grouped with any continent at all. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Boundaries between continents」の詳細全文を読む スポンサード リンク
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