Like a circle, a ball has a center, which is called the center of the ball.
In mathematics, the meaning of projection refers to the establishment of the corresponding relationship between two surface point sets. In cartography, map projection refers to the establishment of a one-to-one correspondence between two point sets, that is, the method and process of studying how to represent the earth's surface on the map plane.
Importance-Correct map projection is the basis of synthesizing/overlaying spatial data from different sources. If you don't understand map projection, you can't use GIS software to solve practical problems!