This mandala is a representation of the movements of the planets and the whole cosmos around Mount Meru, the holy mountain considered the center of the axis of both the physical and spiritual universe.
There are several thangka paintings that feature mount Meru (also called “Sumeru”) with different designs. It is often represented with geometric shapes that are symbols of the different metaphysical state of the mind according to traditional Tibetan Buddhism.
In this case, the mountain is seen from the sky and appears as a small point decorated with an “om” symbol in the center of the mandala.