Northern Ireland is an integral part of the United Kingdom of Great Britain and Northern Ireland, situated in the northeastern portion of the island of Ireland. Northern Ireland is bounded on the north and northeast by the North Channel, on the southeast by the Irish Sea, and on the south and west by the Republic of Ireland. It includes Rathlin Island in the North Channel and several smaller offshore islands. Northern Ireland is also known as Ulster, because it comprises six of the nine counties that constituted the former province of Ulster. The total area of Northern Ireland is 14,148 sq km.
The country consists mainly of a low, flat plain in the approximate center of which is Lough Neagh, the largest lake in the British Isles. Other important lakes are Lough Erne and Upper Lough Erne. Apart from several isolated elevations, three major areas of considerable height are the Sperrin Mountains in the northwest, the Antrim Plateau along the northeastern coast, and the Mourne Mountains in the southeast. The highest point in the country is Slieve Donard, a peak in the Mourne Mountains.