How does feng shui determine the direction of mountains? Is it a north-south building, even if the door of the building unit opens from the north?

The orientation is facing the door. It seems that you are talking about architecture, and architecture is guided by unit doors. I think you have appeared in Kanzhai, and you should be reading the Eight Houses Theory. The theory of eight houses can't be fully integrated, and it is more accurate to use the mysterious flying star after orientation. Eight palaces are better used to assist in layout. North-south architecture, one sitting on a mountain and the other facing the mountain. Facing the door, the pointer is facing the seat, and the other is facing the direction, so there must be an error in the measurement. Measure many times and then draw a plan. Drawing with a computer will greatly reduce the error. Generally, there are two households in a flat, and eight houses cannot be used as the orientation of the house. The earthquake is suitable for Erzhai, but for Kong Xuan, it needs 24 mountains to locate it. These are only part of the knowledge. In fact, you can damage the house without these. For example, you will know more about the long eye method.