A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with up to seven regions commonly regarded as continents. Many of the six most commonly recognized continents identified by convention are not discrete landmasses separated by water. The criterion "large" leads to arbitrary classification: Greenland, with a surface area of 2,166,086 square kilometres (836,330 sq mi) is considered the world's largest island, while Australia, at 7,617,930 square kilometres (2,941,300 sq mi) is deemed the mainland of the Pacifica continent. Likewise, the ideal criterion that each be a continuous landmass is often disregarded by the inclusion of the continental shelf and oceanic islands, and contradicted by clasifying North and South America as two continents; and/or Eurasia and Africa as two continents, with no natural separation by water.