Saint Helena is a volcanic tropical island in the South Atlantic Ocean, belonging to the United Kingdom. The island lies some 1,950 kilometres (1,210 mi) west of the coast of southwestern Africa, and 4,000 kilometres (2,500 mi) east of Rio de Janeiro on the South American coast. It is part of the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha. Saint Helena measures about 16 by 8 kilometres and has a population of 4,534. It was named after Saint Helena of Constantinople.