Boundaries between the continents of Earth

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")[4] 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 Morocco solely.

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.

• Differing boundaries between Europe and Asia
• 
  Conventions used for the boundary between Europe and Asia during the 18th and 19th centuries. The red line shows the most common modern convention, in use since c. 1850 (see below).

    Europe

    Asia

    historically placed in either continent
• 
  Red line "A" was commonly accepted in Russia and Kazakhstan during the Soviet Union era. The commonly accepted modern definition mostly fits with the lines "B" and "F" in this image.
• 
    Transcontinental states, European territory

    Transcontinental states, Asian territory

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.[5]

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.[6] As geographic knowledge of the Greeks increased during the Hellenistic period,[7] 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,[8] Strabo[9] and Ptolemy.[10]

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.[11][12] The mapmakers continued to differ on the boundary between the lower Don and Samara well into the 19th century. The 1745 atlas 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,[12][13] 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.[14]

In Russia and the Soviet Union, the boundary along the Kuma–Manych Depression was the most commonly used as early as 1906.[15] 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,[16] thus placing the Caucasus entirely in Asia and the Urals entirely in Europe.[17] However, most geographers in the Soviet Union favoured the boundary along the Caucasus crest[18] and this became the standard convention in the latter 20th century, although the Kuma–Manych boundary remained in use in some 20th-century maps.

Atyrau, Kazakhstan

Pedestrian bridge over the Ural River in Orenburg. The bridge is between Europe and Asia

Road sign on the continental border between Europe and Asia near Magnitogorsk, Ural Mountains, Russia. It reads "Europe", above a crossed-out "Asia", as one enters Europe and leaves Asia

The modern border between Asia and Europe remains 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.[19][20] 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.[21]

Though most geographic sources assign the area south of the Caucasus Mountain crest to Southwest or Western Asia,[22] 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.[23]

The Turkish city Istanbul lies in on both sides of the Bosporus (one of the Turkish Straits), making it a transcontinental city. Russia and Turkey are transcontinental states with territory in both Europe and Asia by any definition, except for that of Eurasia as a single continent. While Russia is historically, culturally, and politically a European state, with a history of imperial conquests in Asia. The situation for Turkey is inverse, as that of an Asian state with imperial conquests in Europe. Kazakhstan is also a transcontinental state by this definition, its West Kazakhstan and Atyrau provinces extending on either side of the Ural River.[24]

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,[19][24][25] is the most prominent natural feature in the region, and is the "most satisfactory of those (options) proposed"[26] 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.[27]

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.[28] 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):[29]

• listed as part of Eastern Europe: Russian Federation
• listed as part of Central Asia: Kazakhstan
• listed as part of Western Asia: Armenia, Azerbaijan, Cyprus, Georgia, and Turkey

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".[30] 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.[31][32]

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.[33]

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.

Maps

Map	Description
	Map of the world according to Anaximander (6th century BC). Only the parts of Europe, Asia and Africa directly adjacent to the Mediterranean and the Black Sea are known. The Phasis River of the Caucasus in Georgia is imagined as separating Europe from Asia, while the Nile separates Asia from Africa (Libya).
	In this 1570 map of Asia (Asiae Nova Descriptio), the Tanais is used as continental boundary. Moscovia is represented as "transcontinental", having an Asiatic and a European part (labelled Europae pars).
	This 1719 map of "ancient Asia" (Asia Vetus) divides Sarmatia into Sarmatia Europea and Sarmatia Asiatica. The continental boundary is drawn along the Tanais (Don), the Volga and the Northern Dvina.
	Herman Moll (c. 1715) draws the boundary along the Don, the Volga, cutting across land from Samara to the Tobol River, following the lower Irtysh and finally the Ob River, placing Novaya Zemlya in Europe.
	A German map of 1730 by Johann Christoph Homann has a similar boundary to the one shown by Moll, but following the full length of the Samara bend and then cutting across to the Irtysh directly, placing the Tobol and Tobolsk in Asia.
	The "Academy Atlas" of the Russian Empire, published by The Saint Petersburg Academy of Sciences in 1745, draws the boundary along the Don, but then west of the Volga to Arkhangelsk
	1803 Cedid Atlas (Ottoman Empire), draws the boundary along the Don, Volga and River Kama and then cuts northwards to Khaypudyr Bay. Novaya Zemlya is in Europe.
	1806 map of Asia by John Cary, boundary along the Don and then the Volga until Samara, and north of Perm following the Urals, placing Novaya Zemlya in Asia.
	1827 map by Anthony Finley, showing the boundary as running along the Don, the Volga, passing between Perm and Ufa, and running north over land to the Sea of Kara, placing Novaya Zemlya in Europe.
	1861 map by A. J. Johnson, illustrating the modern convention, Caucasus crest, Ural River, Urals.
	1914 map showing the boundary along the Manych River, placing Stavropol Krai in Asia
	Miles Clark in his 1992 "circumnavigation of Europe" followed the White Sea – Baltic Canal until Lake Onega and the Volga–Baltic Waterway to the Rybinsk Reservoir before joining the classical boundary along the Volga and Don rivers.[34][35]

Panama with the Panama Canal

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.[37]

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.