Xianyang () is a prefecture-level city in central Shaanxi province, situated on the Wei River a few kilometers upstream (west) from the provincial capital of Xi'an. Once the capital of the Qin dynasty, it is now integrated into the Xi'an metropolitan area, one of the main urban agglomerations in northwestern China, with more than 7.17 million inhabitants. Its built-up area, consisting of 2 urban districts (Qindu and Weicheng), had 945,420 inhabitants at the 2010 census. It has a total area of . Xianyang is the seat of the Xi'an Xianyang International Airport, the main airport serving Xi'an and the largest airport in Northwest China, and one of the 40 busiest airports in the world. Xianyang is one of the top 500 cities in the world by scientific research outputs, as tracked by the Nature Index. It is home to the main campus of Northwest A&F University (NWAFU), one of the world's top universities in agriculture science related fields, and a member of "Project 985" club which is an organization of 39 reputable universities in China. Xianyang was among the capital city's environs during the Western Zhou dynasty, and was made the capital of the state of Qin in 350 BC during the Warring States period before becoming the capital of China during the short-lived Qin dynasty. Because the city lay south of the Jiuzong Mountains and north of the Wei River – both sunlight-rich (yang) orientations – it was named "Xianyang", meaning "fully yang". Under Duke Xiao of Qin's reign, minister Shang Yang designed Xianyang and in 350 BC organized the relocation of Qin's administration from the old capital Yueyang to the new city, which was then the capital for over 140 years. It was located in the modern day Shaanxi province on the northern bank of the Wei River, on the opposite side of which Liu Bang would later build the Han dynasty capital of Chang'an once he became emperor. In 221 BC, Qin Shi Huang eliminated all six other warring states to establish the first centralized empire in Chinese history.