Without proof, we can give a theorem that the gravity of the earth changes continuously, which is obvious. Then, if the gravity of the earth is 0 and the gravity at infinity is 0, it can be proved that there is a place with the greatest gravity of the earth. Where is this position? In addition to the centrifugal force, the place where gravity plays the greatest role is the metal mines at the two poles. The Arctic is covered with ice and snow, and there are no mineral deposits on the surface of Wang Yang sea, so the maximum gravity is located on the giant magnetite in the north of Lake Mountain in the south of Prince Charles Mountain in Antarctica.
As for where the gravity is weakest on the earth, it can be seen from the above deduction that only the surface of the earth has the concept of "the place with the weakest gravity", that is, the equatorial ocean surface. However, the position of this gravity minimum point is constantly moving and orbiting the earth with the tidal gravity of the moon. If we relax the problem to the whole earth, then the place with the weakest gravity is the center of the earth, where the gravity is 0.