In the early years of the twenty-first century North America received about 10 per cent of the world’s international tourist arrivals and accounted for almost a quarter of the world’s hotel capacity. From a visitor’s point of view the size of the continent is important – extending over eight time zones and including most of the world’s climates – but equally important is the rich variety of landforms and ecosystems. The western part of North America is dominated by high mountain chains, including the spectacular scenery of the Rockies and the Sierra Nevada. Near the eastern seaboard rise the forested Appalachians, much lower in altitude than the Rockies. Between these two mountain systems lie vast interior plains, drained by great rivers such as the Mississippi and its tributaries in the south, and by the St Lawrence, Athabasca and Mackenzie in the north.