Map of North Ireland

 Northern Ireland occupies about one-sixth of the island of Ireland and is separated on the east from Scotland, another part of the United Kingdom, by the narrow North Channel, which is at one point only 13 miles (21 km) wide. The Irish Sea separates Northern Ireland from England and Wales on the east and southeast, respectively, and the Atlantic Ocean lies to the north. The southern and western borders are with the republic of Ireland.

Northern Ireland can be thought of topographically as a saucer centred on Lough (lake) Neagh, the upturned rim of which forms the highlands. Five of the six historic counties—Antrim, Down, Armagh, Tyrone, and Londonderry—meet at the lake, and each has a highland region on the saucer’s rim. To the north and east the mountains of Antrim (physiographically a plateau) tilt upward toward the coast. They reach an elevation of 1,817 feet (554 metres) at Trostan, with the plateau terminating in an impressive cliff coastline of basalts and chalk that is broken by a series of the glaciated valleys known as glens, which face Scotland and are rather isolated from the rest of Northern Ireland. The rounded landscape of drumlins—smooth, elongated mounds left by the melting ice of the final Pleistocene glaciation—in the southeast is punctuated by Slieve Croob, which rises to 1,745 feet (532 metres), and culminates in the Mourne Mountains, which reach an elevation of 2,789 feet (850 metres) at Slieve Donard (Northern Ireland’s highest point) within 2 miles (3 km) of the sea. This impressive landscape of granite peaks is bounded by Carlingford Lough to the south.

The scenery to the south of Lough Neagh is gentler, but the land rises to 1,886 feet (575 metres) in Slieve Gullion near the border with Ireland. West of Lough Neagh the land rises gently to the more rounded Sperrin Mountains; Sawel, at 2,224 feet (678 metres), is the highest of several hills over 2,000 feet (610 metres). The far southwest, the historic County Fermanagh, is focused geographically on the basin of Lough Erne, in a drumlin-strewn area ringed by hills more than 1,000 feet (300 metres) high.