With mountains to the south and water to the north, why is Xi'an built south of the Weihe River and north of the Qinling Mountains?

That’s what you said, but transportation was inconvenient in ancient times. North of the Wei River was basically a plain. Xi’an’s location has the following advantages: 1. Great geographical location, at the foot of the Qinling Mountains and on the Wei River. The thousand-year-old ancient capital of Binhai has the stronghold of Tongguan in the east and the danger of dispersing the pass in the west. In the north, the Chi Road built by the Qin Dynasty, which is hundreds of meters wide and stretches for thousands of miles, leads directly to the Mongolian grassland. It is the main artery for fighting against the Xiongnu and supplying supplies. In the south, there are Ziwu Road, Fanluo Road, Baoxie Road and Chencang Road that can cross Hanzhong. Arriving at Bashu; the Wuguan Road in the Shangluo Mountains in the southeast is the throat leading to the Chu Land. In ancient times, Chang'an had convenient transportation, both land and water, and a dangerous terrain that was easy to defend and difficult to attack. It has always been a battleground for military strategists and a place for emperors to successfully establish their careers. 2. Small environment. Ancient people liked to build cities close to mountains and rivers, with the Qinling Mountains in the south and the Weishui River in the north. In fact, according to Feng Shui, it is a place where energy gathers.

Purely my personal opinion, don’t be offended if I’m wrong