Tajikistan is nestled between Kyrgyzstan and Uzbekistan to the north and west, China to the east, and Afghanistan to the south. Mountains cover 93 percent of Tajikistan's surface area. The two principal ranges, the Pamir Mountains and the Alay Mountains, give rise to many glacier-fed streams and rivers, which have been used to irrigate farmlands since ancient times. Central Asia's other major mountain range, the Tian Shan, skirts northern Tajikistan. Mountainous terrain separates Tajikistan's two population centers, which are in the lowlands of the southern (Panj River) and northern (Fergana Valley) sections of the country. Especially in areas of intensive agricultural and industrial activity, the Soviet Union's natural resource utilization policies left independent Tajikistan with a legacy of environmental problems. Dimensions and borders With an area of , Tajikistan has a maximum east-to-west extent of , and a maximum north-to-south extent of . The country's highly irregular border is long, including along the Chinese border to the east and along the frontier with Afghanistan to the south. Most of the southern border with Afghanistan is defined by the Amu Darya (darya is the Persian word for river) and its tributary the Panj River (Darya-ye Panj), which has headwaters in Afghanistan and Tajikistan. The other neighbors are the former Soviet republics of Uzbekistan (to the west and the north) and Kyrgyzstan (to the north). Topography and drainage The lower elevations of Tajikistan are divided into northern and southern regions by a complex of three mountain chains that constitute the westernmost extension of the massive Tian Shan system. Running essentially parallel from east to west, the chains are the Turkestan, Zeravshan (Zarafshan), and Hisor (Gissar) mountains. The last of these lies just north of the capital, Dushanbe, which is situated in west-central Tajikistan. More than half of Tajikistan lies above an elevation of . Even the lowlands, which are located in the Fergana Valley in the far north and in Khatlon Province in the southwest, are well above sea level. In the Turkestan range, highest of the western chains, the maximum elevation is . The highest elevations of this range are in the east, near the border with Kyrgyzstan. That region is dominated by the peaks of the Pamir-Alay mountain system, including two of the three highest elevations in the former Soviet Union: Mount Lenin — and Ismoil Somoni Peak — . Several other peaks in the region also exceed . The