Why are there no Xi 'an among the six geomantic treasures in China?

Xi 'an's name is named according to the geomantic theory of Yi-ology. According to geomantic theory, two geomantic "situations" are the geomantic treasures of Shangji, namely "dislocation" and "depression". "Lingbi" refers to the intersection of major rivers and tributaries, and "concave" refers to the surrounding position of river bends. Cities named after the word "an" are all based on the theory of "four gods and sands" in Feng Shui, and the local area should be surrounded by mountains on three sides and water on one side. For example, "Yan 'an" is also formed by the beachhead formed by the intersection of the Yellow River and the Yanhe River.