Longnan is in southern Gansu province bordering Shaanxi in the east and Sichuan in the south. It is called Gansu's southern gateway and gateway to the northwest. The major geographic features in Longnan are the Qinba Mountains in the east, the Loess Plateau in the north, and the Tibetan Plateau in the west. It is part of the Central Han basin in the east and the Sichuan basin in the south. Elevations range from 800 to 4,200 m (2,620 to 13,780 ft) above sea level. The three major rivers in Longnan are the Bailong, the Baishui, and the Jialing. Besides these major rivers there are more than 3800 streams and creeks. The annual flow from all of these rivers and streams is more than 28 billion m3. The area of the prefecture is 27,000 square kilometres (10,000 sq mi).
Longnan has a temperate, monsoon-influenced semi-arid climate (Köppen BSk/BSh, depending on the source definition), with cool and very dry winters and hot, moderately humid summers. Due to the protected valley location and the southerly location in the province, the area is one of the warmest in Gansu, with annual temperatures ranging from 10 to 15 °C (50 to 59 °F). The annual precipitation is 400 to 1,000 mm (16 to 39 in), while there are between 160 to 280 frost free days. With monthly percent possible sunshine ranging from 34% in September and October to 53% in December, the city receives 1,850 sunlight hours annually. Two-thirds of the annual rainfall occurs from June to September. At Wudu, the monthly 24-hour average temperature ranges from 3.3 °C (37.9 °F) in January to 24.8 °C (76.6 °F) in July, the annual mean is 14.63 °C (58.3 °F), and the annual precipitation is 472 mm (18.6 in).
Longnan was settled by humans at least 7000 years ago. Between 5000 and 6000 years ago, civilizations developed along the Xihan ("Western Han") and Bailong ("White Dragon") rivers. Anping in Wudu as well as Lixian both have ancient ruins. Longnan is very important in Chinese history: it was the home of Rong tribes that troubled the Shang and Zhou dynasties and is considered the homeland of the House of Ying, the family of the Qin dynasty that united China at the end of the Warring States period. Wudu County was even founded as part of the Qin Empire. It is still common to find Qin artifacts—including pottery, bronzes, and coins—in the area.
During the Sixteen Kingdoms period, the region was ruled by the Qiang kingdoms of Later Qin and Tanchang, the latter has its capital in present-day Tanchang. Tanchang is conquered by Emperor Wu of Northern Zhou in 564. The region then went under control of Sui, Tang and Song dynasties, then subsequently conquered by the Tibetans, Tanguts, Jurchens and Mongols before finally administered by Ming dynasty court.
Longnan has 1 urban districts, 8 counties, 242 towns, and 3243 villages with a total population of 2567718.
In 2004, Longnan's GDP was 6,338,000 RMB, a 12% growth over the previous year.
Important agricultural products include cereals and grains, Chinese medicinal herbs, vegetable oil, fruits, nuts, berries, and vegetables. Coal, copper, lead, zinc, petroleum, and gold are all major mineral resources for Longnan. Cement and other building materials are also produced here.
The Longnan Chengzhou Airport is scheduled to be built to serve the city.
Longnan has more than 1300 species of trees and shrubs, 1300 plants and herbs used for Chinese medicine, 100 wild fruits and berries, and 300 species of animals, many species of which are protected.