Why are the palaces where the Emperor lives also called Wei Zi Palace and Forbidden City?

There are some stars on each side of the three walls as a frame, which defines the scope of these three sky areas. They seem to be walls, so they are called walls. Of the three walls, the Ziwei Courtyard is the center of heaven and the place where the Emperor of Heaven lives. Therefore, the palaces where the Emperor lives are also called Wei Zi Palace and Forbidden City.