The total area of the United Kingdom is approximately . The country occupies the major part of the British Isles archipelago and includes the island of Great Britain, the north-eastern one-sixth of the island of Ireland and some smaller surrounding islands. It lies between the North Atlantic Ocean and the North Sea with the southeast coast coming within  of the coast of northern France, from which it is separated by the English Channel. In 1993 10 per cent of the UK was forested, 46 per cent used for pastures and 25 per cent cultivated for agriculture. The Royal Greenwich Observatory in London was chosen as the defining point of the Prime Meridian in Washington, DC, in 1884, although due to more accurate modern measurement the meridian actually lies 100 metres to the east of the observatory.