Determining the boundaries between the continents is generally a matter of geographical convention and consensus. 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:
