<P> 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 . </P> <P> There are three overland boundaries subject to definition: </P> <Ul> <Li> 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) </Li> <Li> between Asia and Africa (dividing Afro - Eurasia into Africa and Eurasia): at the Isthmus of Suez </Li> <Li> between North America and South America (dividing the Americas): the Isthmus of Panama </Li> </Ul> <Li> 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) </Li>

Where is the line between north and south america