The topography of the United Kingdom is generally divided into lowland and highland zones, often separated by the Tees-Exe line—an imaginary line running from the River Tees in the northeast of England to the River Exe in the southwest.
North and west of this line, the landscape is predominantly highland. The Scottish Highlands contain the most rugged and mountainous terrain in the UK, including the highest peak, Ben Nevis, which stands at 1,345 meters (4,413 feet). The Pennines, often referred to as the "backbone of England," run down the center of Northern England. Wales is characterized by the Snowdonia massif, peaking at Mount Snowdon (1,085 meters). Northern Ireland features the Sperrin Mountains and the Mourne Mountains.
South and east of the Tees-Exe line, the terrain flattens into undulating plains, low hills, and fertile valleys. Key topographic features here include the Cotswolds, the Chiltern Hills, and the chalk escarpments of the North and South Downs, which terminate at the famous White Cliffs of Dover. The lowest point in the UK is Holme Fen in Cambridgeshire, lying 2.75 meters (9 feet) below sea level within a vast plain of drained marshland known as the Fens.