Ireland is an island in Northwestern Europe in the north Atlantic Ocean. The island lies on the European continental shelf, part of the Eurasian Plate. The island's main geographical features include low central plains surrounded by coastal mountains. The highest peak is Carrauntoohil , which is 1,039 meters (3,409 ft) above sea level. The western coastline is rugged, with many islands, peninsulas, headlands and bays. The island is bisected by the River Shannon, which at 360.5 km (224 mi) with a 102.1 km (63 mi) estuary is the longest river in Ireland and flows south from County Cavan in Ulster to meet the Atlantic just south of Limerick. There are a number of sizeable lakes along Ireland's rivers, of which Lough Neagh is the largest. Politically, the island consists of the Republic of Ireland, with jurisdiction over about five-sixths of the island, and Northern Ireland, a constituent country of the United Kingdom, with jurisdiction over the remaining sixth. Located west of the island of Great Britain, it is located at approximately 53°N 8°WCoordinates: 53°N 8°W. It has a total area of 84,421 km2 (32,595 sq mi). It is separated from Great Britain by the Irish Sea and from mainland Europe by the Celtic Sea. Ireland forms the second largest landmass in the North-West European Archipelago, together with nearby islands including Great Britain and the Isle of Man, known in the United Kingdom as the British Isles.