The Republic of Kiribati, formerly known as the Gilbert Islands and a former colony of the United Kingdom, comprises three groups of 33 atoll islands scattered astride both the Equator and the International Date Line. It has the distinction of being the only country to occupy the four corners of the globe. Inclusive of its 200-mile (322-kilometre) Exclusive Economic Zone, it covers 1.3 million square miles (3.5 million square kilometres) of the centre of the Pacific Ocean, in contrast to its total landmass of just over 800 square kilometres (309 square miles). Atoll islands are coral islands that form atop submerged seamounts, typically aligned as a string according to the movement of the tectonic plate where they are located and the hotspots beneath the plate, which burn through the plate to form the seamounts. The islands are narrow strips of coral sand surrounding a lagoon, and are low lying, on average rising no more than 2 metres (6.5 feet) above sea level.