In China's metaphysics, what position does "Zhonggong" refer to?

The palace is purple, living in the center of the northern sky.

Ziweiyuan is the middle wall of three yuan, living in the center of the northern sky, so it is also called Zhonggong, or Ziweiyong. Wei Zi Palace means Imperial Palace, and most stars are named after official names. It is located in the center of the north, with 15 stars in the east and 15 stars in the west. The two bows were joined together and surrounded by a wall. According to the observation records of Ziweiyuan during the Song You period, * * * has 37 constellations with 2 additional stars, 163 positive stars and 18 1 additional stars. Its sky area is roughly equivalent to the international constellations of Bear, Bear, Dragon, Hound, Mu Fu, Unbounded Constellation, Wang Xianxing, Hou Xian Constellation, Yingxian Constellation and Lubao Constellation.