Xuanwu Mountain is actually the origin and development. The whole dragon body was cut off. In ancient times, Yuan Tiangang, on behalf of the royal family, searched the whole country for the Long Mai that could be produced, and then cut it off to prevent the real dragon emperor from endangering the throne. There are many such stories.
Modern Long Mai was destroyed intentionally or unintentionally. Whether it's a house in the Yang or a house in the Yin, it's not good for people from the perspective of geomantic omen.