Altitude describes a person's height and weight.

For example, this sea is high or that so-and-so is too low.

It's ridiculous to be tall. Actually, altitude is not used like this. Altitude refers to the vertical distance above the altitude of a place on the ground.

On the Internet, the word altitude is often used to represent a person's height. Geographical height refers to the vertical distance above or below the sea level of a certain place or geographical thing on the ground, which is the abbreviation of altitude.

It is relative to the relative height, and the reference base point for calculating the altitude is to confirm a recognized sea level for calculation. This sea level is equivalent to the 0 scale in the scale. So altitude is also called absolute altitude or absolute altitude.

Relative height is the height difference between two points. However, the sea surface ebbs and flows, and the big waves and small waves keep on. It can be said that there has never been a moment of calm, and there are obvious differences in the sea level between high tide and low tide every month. Therefore, people think that only a certain average sea level can be used as the starting surface of altitude. Altitude is defined as the height above or below the average sea level.

This is what people usually call altitude or absolute altitude. Due to the inhomogeneity of mass inside the earth, the gravity lines of all points on the earth's surface do not all point to the center of the sphere. In this way, the geoid perpendicular to the gravity line forms irregular surfaces everywhere. So all countries in the world have their own average sea level, that is, the geoid.