China's traditional four directions, southeast and northwest, are symbolized by peacock, snake turtle, dragon and white tiger. The gate facing south is Zhuque Gate, the gate facing north is Xuanwu Gate, the gate facing east is Qinglong Gate, and the gate facing west is Baihu Gate. The formula means "former Suzaku, later Xuanwu, left Qinglong, right White Tiger".
A friend of mine knows this. Listen to him.