Boundaries between the continents of Earth

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 Afro-Eurasia and the Americas are each considered a single continent. An island can be considered to be associated with a given continent by either lying on the continent's adjacent continental shelf (e.g. Singapore, the British Isles) or being a part of a microcontinent on the same principal tectonic plate (e.g. Madagascar and Seychelles). An island can also be entirely oceanic while still being associated with a continent by geology (e.g. Bermuda, the Australian Indian Ocean Territories) or by common geopolitical convention (e.g. Ascension Island, the South Sandwich Islands). Another example is the grouping into Oceania of the Pacific Islands with Australia and Zealandia.
There are three overland boundaries subject to definition:
While the isthmus between Asia and Africa and that between North and South America are today navigable, via the Suez and Panama canals, respectively, diversions and canals of human origin generally are 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:
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 and from Africa, and is usually grouped with Europe if grouped with any continent. By contrast, the Canary Islands and the Madeira islands (the latter of which also include the Desertas Islands and the Savage Islands) off the Atlantic coast of Morocco are much closer to, and usually grouped with, Africa; the Canary Islands are only from the African coast at their closest point but from the European coast, while Madeira is from Africa and from Europe.
The Mediterranean island nation of Malta is about from the coast of Sicily in Europe - much closer than the distance to the closest African coast. The nearby Italian island of Lampedusa (principal island of the Pelagie Islands) is from Sicily while just from the African coast; similarly, Pantelleria is from Sicily and just from the African coast. All of these Mediterranean islands are actually located on the African plate, and may be considered part of the continent of Africa. However, for political and historical reasons, maps generally display them as part of Europe. A single Spanish islet, known as Alboran Island, is also debatably located on either the African plate or the Eurasian plate. This island is located in the Alboran Sea, 50 km (31 mi) north of the Moroccan coast and 90 km (56 mi) south of Spain.
European-governed territory in Africa.
There are six definitive occurrences of territories unequivocally being a part of the African continent, but legally being administered by a European state. Three of these are administered by France, and three of these are administered by Spain. The existence of these territories further blurs the line between the borders of Africa and Europe, in particular with regard to the Spanish territories which lie immediately adjacent to and/or connected to the African mainland. The French territories lie within the Indian Ocean, and, consequently, are more dislocated from the principal boundary between the two continents.
The uninhabited Spanish unincorporated overseas minor territories, known as the plazas de soberanía ("Localities of Sovereignty"), are small islands that lie immediately adjacent to the North African coastline, with the exception of Peñón de Vélez de la Gomera, which was originally an island like the other 'localities' but has subsequently become directly connected to the Moroccan (African) coastline. The two other Spanish territories are the exclaves of Ceuta and Melilla, which are two populated coastal cities located directly on the African mainland, both bordering only Morocco.
Two of the French territories are the inhabited overseas departments and regions of Réunion and Mayotte. Réunion is an island territory located near the island nation of Mauritius and to the east of island nation of Madagascar (both nominally considered a part of the African continent). Mayotte is an island territory located west of Madagascar within the Mozambique Channel. The final territory is the Scattered Islands in the Indian Ocean, administratively a part of the French Southern and Antarctic Lands. This French territory consists of a range of minor uninhabited island atolls in the Indian Ocean, located in the deep sea surrounding Madagascar.
Europe and Asia.
The boundary between Europe and Asia is unusual among continental boundaries because of its largely mountain-and-river-based characteristics north and east of the Black Sea. The reason is historical, the division of Europe and Asia going back to the early Greek geographers.
In the modern sense of the term "continent", Eurasia is more readily identifiable as a "continent", and Europe has occasionally been described as a subcontinent of Eurasia.
History.
The threefold division of the Old World into Europe, Asia and Africa has been in use since the 6th century BC, due to early Greek geographers such as Anaximander and Hecataeus.
Anaximander placed the boundary between Asia and Europe along the Phasis River (the modern Rioni) in the Caucasus (from its mouth by Poti on the Black Sea coast, through the Surami Pass and along the Kura River to the Caspian Sea), a convention still followed by Herodotus in the 5th century BC.
As geographic knowledge of the Greeks increased during the Hellenistic period, this archaic convention was revised, and the boundary between Europe and Asia was now considered to be the Tanais (the modern Don River). This is the convention used by Roman era authors such as Posidonius, Strabo and Ptolemy.
Throughout the Middle Ages and into the 18th century, the traditional division of the landmass of Eurasia into two continents, Europe and Asia, followed Ptolemy, with the boundary following the Turkish Straits, the Black Sea, the Kerch Strait, the Sea of Azov and the Don (known in antiquity as the Tanais). But maps produced during the 16th to 18th centuries tended to differ in how to continue the boundary beyond the Don bend at Kalach-na-Donu (where it is closest to the Volga, now joined with it by the Volga–Don Canal), into territory not described in any detail by the ancient geographers.
Philip Johan von Strahlenberg in 1725 was the first to depart from the classical Don boundary by drawing the line along the Volga, following the Volga north until the Samara Bend, along Obshchy Syrt (the drainage divide between Volga and Ural) and then north along Ural Mountains. The mapmakers continued to differ on the boundary between the lower Don and Samara well into the 19th century. The published by the Russian Academy of Sciences has the boundary follow the Don beyond Kalach as far as Serafimovich before cutting north towards Arkhangelsk, while other 18th- to 19th-century mapmakers such as John Cary followed Strahlenberg's prescription. To the south, the Kuma–Manych Depression was identified circa 1773 by a German naturalist, Peter Simon Pallas, as a valley that, once upon a time, connected the Black Sea and the Caspian Sea, and subsequently was proposed as a natural boundary between continents.
By the mid-19th century, there were three main conventions, one following the Don, the Volga–Don Canal and the Volga, the other following the Kuma–Manych Depression to the Caspian and then the Ural River, and the third abandoning the Don altogether, following the Greater Caucasus watershed to the Caspian. The question was still treated as a controversy in geographical literature of the 1860s, with Douglas Freshfield advocating the Caucasus crest boundary as the best possible, citing support from various modern geographers.
In Russia and the Soviet Union, the boundary along the Kuma–Manych Depression was the most commonly used as early as 1906. In 1958, the Soviet Geographical Society formally recommended that the boundary between the Europe and Asia be drawn in textbooks from Baydaratskaya Bay, on the Kara Sea, along the eastern foot of Ural Mountains, then following the Ural River until the Mugodzhar Hills, and then the Emba River; and Kuma–Manych Depression, thus placing the Caucasus entirely in Asia and the Urals entirely in Europe. However, most geographers in the Soviet Union favoured the boundary along the Caucasus crest and this became the standard convention in the latter 20th century, although the Kuma–Manych boundary remained in use in some 20th-century maps.
Modern definition.
The modern border between Asia and Europe is a historical and cultural construct, defined only by convention. The modern border follows the Aegean Sea, the Dardanelles–Sea of Marmara–Bosphorus (together known as the Turkish Straits), the Black Sea, along the watershed of the Greater Caucasus, the northwestern portion of the Caspian Sea and along the Ural River and Ural Mountains to the Kara Sea, as mapped and listed in most atlases including that of the National Geographic Society and as described in The World Factbook. According to this definition, Georgia and Azerbaijan both have most of their territory in Asia, although each has small parts of their northern borderlands north of the Greater Caucasus watershed and thus in Europe.
Though most geographic sources assign the area south of the Caucasus Mountain crest to Southwest or Western Asia, no definition is entirely satisfactory, with it often becoming a matter of self-identification. Cultural influences in the area originate from both Asia and Europe. While geographers rarely define continents primarily politically, Georgia and to a lesser extent Armenia and Azerbaijan are increasingly in the 21st century politically oriented towards Europe, but Armenia has a great cultural diaspora to the south, and Azerbaijan shares a cultural affinity with Iranian Azerbaijan as well as with the Turkic states of Central Asia.
Russia and Turkey are transcontinental states with territory in both Europe and Asia. While Russia is historically, culturally, and politically a European state, with a history of imperial conquests in Asia. Conversely, the situation for Turkey is the inverse, that of an Asian state with imperial conquests in Europe. Kazakhstan is also a transcontinental state by this definition, with its West Kazakhstan and Atyrau provinces extending on either side of the Ural River. The Turkish city Istanbul is a transcontinental city due to its location on both sides of the Bosporus (one of the Turkish Straits).
This Ural River delineation is the only segment not to follow a major mountain range or wide water body, both of which often truly separate populations. However, the Ural River is the most common division used by authorities, is the most prominent natural feature in the region, and is the "most satisfactory of those (options) proposed" which include the Emba River, a much smaller stream cutting further into Central Asian Kazakhstan. The Ural River bridges in Atyrau and Orenburg are even labeled with permanent monuments carved with the word "Europe" on one side, "Asia" on the other.
The Kuma–Manych Depression (more precisely, the Manych River, the Kuma–Manych Canal and the Kuma River) remains cited less commonly as one possible natural boundary in contemporary sources. This definition peaked in prominence in the 19th century, however it has declined in usage since then, as it places traditionally European areas of Russia such as Stavropol, Krasnodar, and even areas just south of Rostov-on-Don in Asia.
One formal means by which states are grouped into one specified continental area or another is by using the definition used for statistical purposes by the United Nations Statistics Division (UNSD):
According to UNSD, the aforementioned "assignment of countries or areas to specific groupings is for statistical convenience and does not imply any assumption regarding political or other affiliation of countries or territories". Furthermore, the UNSD classification often differs from those of other United Nations organizations. For instance, while UNSD includes Georgia and Cyprus in Western Asia, the United Nations Industrial Development Organization and UNESCO include both states in Europe.
The Council of Europe includes the Eurasian states of Armenia, Azerbaijan, Cyprus, Georgia, Russia, and Turkey. It notes that
[T]wo Council of Europe member States, Turkey and Russia, belong geographically to both Europe and Asia and are therefore Eurasian. Strictly speaking, the three South Caucasus States, Armenia, Azerbaijan and Georgia are located in Asia, yet their membership of political Europe is no longer in doubt.
Islands.
Cyprus is an island of the Mediterranean located on the Asian continental shelf, geologically a part of the Anatolian Plate and adjacent to Asia Minor, by which it is usually associated with Asia (Western Asia), as in The World Factbook and the United Nations geoscheme, but the Republic of Cyprus was nevertheless admitted to the Council of Europe in 1961 and joined the EU in 2004. The northern part of the island functions as the unrecognized (except by Turkey) Turkish Republic of Northern Cyprus.
The Greek North Aegean Islands and the Dodecanese lie on the coast of the Asian part of Turkey (on the Asian continental shelf). Thus, generally, these island groups could be considered a part of Asia. More specifically, the small islands of Kastellorizo, Strongyli Megistis, and Ro (all these islands are still in the Dodecanese group) are directly to the south of the Turkish Anatolia coastline, of which they are directly adjacent. Additionally, they lie at some distance to the east of the rest of the Dodecanese group in the direction of Cyprus and the Turkish city of Antalya. Akin to Cyprus, these small islets would nominally be considered Asian if only the continental shelf were used to define the boundary, ignoring historical and cultural influences on the boundary.
Russia's Vaygach Island and Novaya Zemlya extend northward from the northern end of the Ural Mountains and are a continuation of that chain into the Arctic Ocean. While Novaya Zemlya was variously grouped with Europe or with Asia in 19th-century maps it is now usually grouped with Europe, the continental boundary considered to join the Arctic Ocean along the southern shore of the Kara Sea. The Russian Arctic archipelago of Franz Josef Land farther north is also associated with Europe.
Europe and North America.
The geographical notion of a continent stands in opposition to islands and archipelagos. Nevertheless, there are some islands that are considered part of Europe in a political sense. This most notably includes the British Isles (part of the European continental shelf and during the Ice Age of the continent itself); the islands of the North Sea, the Baltic Sea, and the Mediterranean that are part of the territory of a country situated on the European mainland; the Azores on the Mid-Atlantic Ridge, part of Portugal; and usually also the island states of Iceland (part of Norway and/or Denmark from 13th to early 20th centuries) and Malta.
The Norwegian islands of Jan Mayen and Svalbard in the Arctic Ocean are usually associated with Europe.
South of the Arctic, Europe and North America are separated by the North Atlantic. In terms of associating its oceanic islands with either continent, the boundary is usually drawn between Greenland and Iceland and between Bermuda and the Azores' (Western Group)—all other North Atlantic islands are continental. Iceland and the Azores are protrusions of the Mid-Atlantic Ridge and are associated with and peopled from Europe, even though they have areas on the North American Plate. (Definitions of "continents" are a physical and cultural construct dating back centuries, long before the advent or even knowledge of plate tectonics; thus, defining a "continent" falls into the realm of physical and cultural geography [i.e., Geopolitics ], while continental plate definitions fall under plate tectonics in the realm of geology.)
Greenland is geographically part of North America. Politically, however, it is more associated with Europe as it is part of the Kingdom of Denmark, although it has extensive home rule and EU law no longer applies there.
Three islands in the Caribbean are legally a direct part of the Netherlands, that is the Caribbean Netherlands (Bonaire, Saba and Sint Eustatius). Two islands in the Caribbean are legally a direct part of France, Guadeloupe and Martinique.
Africa and Asia.
Historically in Greco-Roman geography, "Africa" meant Ancient Libya, and its eastern extent was taken to be around Marmarica, at the "Catabathmus Magnus", placing Egypt in Asia entirely. The idea of Egypt being an "African" country seems to develop in around the mid-19th century; the term "Africa" was classically reserved for what is now known as the Maghreb, to the explicit exclusion of Egypt, but with the exploration of Africa the shape of the African landmass (and Egypt's "natural" inclusion in that landmass) became apparent. In 1806, William George Browne still titled his travelogue "Travels in Africa, Egypt, and Syria". Similarly, James Bruce in 1835 published "Travels through part of Africa, Syria, Egypt, and Arabia". On the other hand, as early as 1670 John Ogilby under the title "Africa" published "an accurate Description of the Regions of Egypt, Barbary, Libya, and Billedulgerid, the Land of Negroes, Guinea, Æthiopia, and the Abyssines, with all the adjacent Islands, either in the Mediterranean, Atlantic, Southern, or Oriental Seas, belonging thereunto".
The usual line taken to divide Africa from Asia today is at the Isthmus of Suez, the narrowest gap between the Mediterranean and Gulf of Suez, the route today followed by the Suez Canal. This makes the Sinai Peninsula geographically Asian, and Egypt a transcontinental country. Less than 2% of Egyptian population live in the Sinai, and hence Egypt, even though technically transcontinental, is usually considered an African country entirely and not partly Asian. But when discussing the geopolitical region of the Middle East and North Africa, Egypt is usually grouped with the Western Asian countries as part of the Middle East, while Egypt's western neighbor Libya is grouped with the remaining North African countries as the Maghreb. Both are members of the African Union.
The Seychelles, Mauritius, and Comoros are island nations in the Indian Ocean associated with Africa. The island of Socotra may be considered African as it lies on its shelf, but is part of Yemen, an Asian country.
North and South America.
Mainland.
The border between North America and South America is at some point on the Isthmus of Panama. The most common demarcation in atlases and other sources follows the Darién Mountains watershed that divides along the Colombia–Panama border where the isthmus meets the South American continent (see Darién Gap). Virtually all atlases list Panama as a state falling entirely within North America and/or Central America.
Islands.
Often the Caribbean islands are considered part of North America, but Aruba, Bonaire, Curaçao (ABC islands), and Trinidad and Tobago lie on the continental shelf of South America. On the other hand, the Venezuelan Isla Aves and the Colombian San Andrés and Providencia lie on the North American shelf. Additionally, the adjacent Venezuelan islands of Nueva Esparta and the islands of the Venezuelan Federal Dependencies can be considered to be a part of the Caribbean instead of part of South America. The circumstance of these islands is akin to that of the ABC islands, as both the ABC islands and the Venezuelan islands are at an equivalent range from the Venezuelan mainland. Thus, these Venezuelan lands could consequently be placed in North America instead.
Asia and North America.
The Bering Strait and Bering Sea separate the landmasses of Asia and North America, as well as forming the international boundary between Russia and the United States. This national and continental boundary separates the Diomede Islands in the Bering Strait, with Big Diomede in Russia and Little Diomede in the U.S. The Aleutian Islands are an island chain extending westward from the Alaskan Peninsula toward Russia's Komandorski Islands and Kamchatka Peninsula. Most of them are always associated with North America, except for the westernmost Near Islands group, which is on Asia's continental shelf beyond the North Aleutians Basin and on rare occasions could be associated with Asia, which could then allow the U.S. state of Alaska to be considered a transcontinental state.
St. Lawrence Island in the northern Bering Sea belongs to Alaska and may be associated with either continent but is almost always considered part of North America, as with the Rat Islands in the Aleutian chain. At their nearest points, Alaska and Russia are separated by only .
The Americas, Australia and Oceania.
The Galápagos Islands and Malpelo Island in the eastern Pacific Ocean are possessions of Ecuador and Colombia, respectively, and associated with South America. The uninhabited French possession of Clipperton Island off the Mexican coast is associated with North America.
Easter Island, also known by its endonym Rapa Nui, is a territory of Chile, and is considered to be in Oceania, though politically it is associated with South America. Similar to Easter Island, and just to the northeast of it, is the nearby uninhabited Salas y Gómez Islands of Chile, which is also considered to be in Oceania while associated with South America politically. Additionally, Chile has the Desventuradas Islands and the Juan Fernández Islands, both are located in the Eastern Pacific and to the East of Salas y Gómez and Easter Island. Akin to Clipperton, the Desventuradas Islands and the Juan Fernández Islands are nominally associated with South America.
The United States controls numerous territories in Oceania, including the state of Hawaii and the territories of Guam, the Northern Mariana Islands and American Samoa.
Asia and Australia.
The continental boundary between Asia and Australia is somewhere in the Wallacean region of the Malay Archipelago. The boundary is most commonly divided along the anthropologic Melanesian Line or the biogeographic Weber's Line. Indonesia administers the western half of New Guinea, geographically a part of the Australian continent. The eastern half of the island is a part of Papua New Guinea which is considered to be a part of Oceania. Indonesia is commonly referred to as one of the Southeast Asian countries. East Timor, an independent state that was formerly a part of Indonesia, which is geographically a part of Asia, is classified by the United Nations as a part of the South-eastern Asia subregion. It is expected to join the Association of Southeast Asian Nations, having been involved as an ASEAN Regional Forum member since independence, and has participated in the Southeast Asian Games since 2003. Occasionally, all of the Malay Archipelago is included in Oceania, although this is extremely rare, especially as most of the archipelago lies on the Asian continental shelf.
Japan possesses the Bonin Islands (also known as the Ogasawara Islands), the Volcano Islands, and three remote islets (Nishinoshima, Minami-Tori-shima and Okinotorishima), all governed collectively as Ogasawara Village, which is an administrative division consisting of scattered island atolls located in the Pacific Ocean. These islands are located at some distance southeast of the Japanese Archipelago. Owing to the location and the oceanic nature of these islands, they are sometimes considered to be a part of Oceania as well.
The Commonwealth of Australia has some island possessions in Zealandia and two external territories in the Indian Ocean, which are closer to Indonesia than to Mainland Australia. Nevertheless, these two island territories are located on the Australian Plate, south of the Sunda Trench.
Antarctica.
Antarctica along with its outlying islands have no permanent population. All land claims south of 60°S latitude are held in abeyance by the Antarctic Treaty System.
Australia's Heard Island and McDonald Islands and the French Kerguelen Islands are located on the Kerguelen Plateau, on the Antarctic continental plate. The French Crozet Islands, Île Amsterdam, Île Saint-Paul, and the Norwegian Bouvet Island are also located on the Antarctic continental plate, and are not often associated with other continents.
The South Georgia and the South Sandwich Islands are closer to Antarctica than to any other continent. However, they are politically associated with the inhabited Falkland Islands, which are closer to South America. Furthermore, Argentina, a South American country, maintains its irredentist claims on the islands. The continental shelf boundary separates the two island groups.
The Prince Edward Islands are located between Africa and Antarctica, and are the territory of South Africa, an African country.
The Australian Macquarie Island and the New Zealand Antipodes Islands, Auckland Islands, and Campbell Islands, are all located between Australia and New Zealand and Antarctica.