In ancient times, people thought that there were nine floors in the sky, also called "Jiuyu". When you visited it for nine days, you can see the vastness of the sky and the space and time around it. As the saying goes, sit quietly and watch the tigers fight, and travel 80,000 miles a day, let alone above the clouds. Therefore, the concept of "nine empty streams" is used to express the emperor who lives in a remote place and has a panoramic view of everything in the world.
This tone is heroic and the realm is high, and only the respect of the emperor can match it. So on weekdays, ordinary people rarely see it.