Scotland comprises the northern one-third of the island of Great Britain as well as 790 surrounding islands encompassing the major archipelagoes of the Shetland Islands, Orkney Islands and the Inner and Outer Hebrides. Scotland contains the majority of mountainous terrain in the UK. The topography of Scotland is distinguished by the Highland Boundary Fault - a geological rock fracture – which traverses the Scottish mainland. The fault line separates two distinctively different physiographic regions; namely the Highlands to the north and west and the Lowlands to the south and east. The more rugged Highland region contains the majority of Scotland's mountainous terrain, including the highest peak, Ben Nevis. Lowland areas, in the southern part of Scotland, are flatter and home to most of the population.