Laos is the only landlocked country in Southeast Asia, and it lies mostly between latitudes 14° and 23°N (a small area is south of 14°), and longitudes 100° and 108°E. Its thickly forested landscape consists mostly of rugged mountains, the highest of which is Phou Bia at , with some plains and plateaus. The Mekong River forms a large part of the western boundary with Thailand, where the mountains of the Annamite Range form most of the eastern border with Vietnam and the Luang Prabang Range the northwestern border with the Thai highlands. There are two plateaux, the Xiangkhoang in the north and the Bolaven Plateau at the southern end. Laos can be considered to consist of three geographical areas: north, central, and south. Laos had a 2019 Forest Landscape Integrity Index mean score of 5.59/10, ranking it 98th globally out of 172 countries.