Scotland is the northernmost region of the four parts of the United Kingdom, and comprises a third of the island of Great Britain. It is surrounded by the waters of the North Sea to the east and the North Atlantic Ocean to the west and north. Its only land border is with England to the southeast, which runs for 97 kilometres (60 miles). Scotland has two distinct topographic (and cultural) regions, divided by the Highland Boundary Fault: the Highlands in the north and west, and the Lowlands in the south and east. The Lowlands in turn is composed of the Midland Valley (Central Lowlands), and the Southern Uplands. As can be discerned from the name, the Highlands are dominated by mountain ranges. While not usually thought of as an island nation, Scotland is in fact made up of more than 700 islands. The islands are mostly in groups to the west (the Inner Hebrides and Outer Hebrides–see “Questions about the Outer Hebrides“). In the North are the Orkney Islands and Shetland Islands.