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

the name of Xi' an is named after the geomantic theory of Yi-ology, and geomantic theory holds that two geomantic "situations" are the geomantic treasures of Shangji, namely "lost position" and "depressed position". "Lingbi" refers to the intersection of major rivers and tributaries, and "Concave" refers to the embracing position of river turning. Cities named after the word "An" are all based on the theory of "Four Gods of Sand" in Feng Shui, and the local area should be surrounded by mountains on three sides and facing the 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.