Archipelagos are usually found in the open sea; less commonly, a big landmass may neighbor them, an example being Scotland which has more than 700 islands surrounding the mainland. Many archipelagos are volcanic, forming along mid-ocean ridges or hotspots. Others are island arcs neighboring an oceanic trench. Many other processes create archipelagos, including erosion, deposition, and land elevation.
The four biggest countries that are mainly archipelagos are Japan, the Philippines, the United Kingdom and Indonesia (the world's biggest archipelagic country according to the CIA World Factbook). The biggest archipelago in the world by size is in Northern Canada, the Canadian Arctic Archipelago, which is in the Arctic Ocean.