Boundaries between the continents
Determining the boundaries between the continents is generally a matter of geographical convention. Several slightly different conventions are in use. The number of continents is most commonly considered seven (in English-speaking countries) but may range as low as four when Afro-Eurasia and the Americas are both considered as single continents. 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: between Africa and Asia (dividing Afro-Eurasia into Africa and Eurasia): at the Isthmus of Suez; between Asia and Europe (dividing Eurasia): along the Turkish straits, the Caucasus, and the Urals and the Ural River (historically also north of the Caucasus, along the Kuma–Manych Depression or along the Don River); between North America and South America (dividing the Americas): at some point on the Isthmus of Panama, with the most common demarcation in atlases and other sources following the Darién Mountains watershed along the Colombia–Panama border where the isthmus meets the South American continent (see Darién Gap). While today the isthmus between Asia and Africa is navigable via the Suez Canal, and that between North and South America via the Panama Canal, these artificial channels are not generally accepted as continent-defining boundaries in themselves. The Suez Canal happens to traverse the isthmus between the Mediterranean Sea and the Red Sea, dividing Africa and Asia.
