The altitude calculated by China is based on Qingdao Yellow Sea. Qingdao is a coastal city with an altitude of 77.2 meters. The altitude of Chengdu is 503 meters. The altitude of Chengdu is much higher than that of Qingdao.

Altitude refers to the vertical distance above the altitude of a place on the ground, which is the height difference between a place and sea level, and is usually calculated based on the average sea level. The sea level in different sea areas is different. In China 1987, it is stipulated that the average sea level of the Yellow Sea calculated by Qingdao tide gauge station after long-term observation should be taken as the datum plane (zero elevation plane). The highest elevation on the earth's surface is Mount Everest (8844.86m), and the lowest elevation is Mariana Trench (-11034m).