The defining factor in the geography of Scotland is the distinction between the Highlands and Islands in the north and west and the Lowlands in the south and east. The Highlands are further divided into the Northwest Highlands and the Grampian Mountains by the fault line of the Great Glen. The Lowlands are divided into the fertile belt of the Central Lowlands and the higher terrain of the Southern Uplands, which included the Cheviot Hills, over which the border with England runs. The Central Lowland belt averages about 50 miles in width, and contains most of the good quality agricultural land. Scotland is half the size of England and Wales in area, but with its many inlets, islands and inland lochs, it has roughly the same amount of coastline at 4,000 miles. Only a fifth of Scotland is less than 60 metres above sea level.