It is one of the Great Russian Regions and has been described as the world's largest unbroken lowland—more than 50 percent is less than 100 metres (330 ft) above sea level—and covers an area of about 2.6– which is about one third of Siberia, extending from north to south for 2,400 km (1,490 mi), from the Arctic Ocean to the foothills of the Altay Mountains, and from east to west for 1,900 km (1,180 mi) from the Ural Mountains to the Yenisei River.