What does gravity mapping show?

Gravity maps are meant to show the difference in the actual gravity field of Earth from the gravity field of featureless Earth surface.

The gravity maps highlights difference in the strength of the gravitational force on the surface of the Earth. For example, mountain ranges causes more gravitational force than on a featureless planet.

Gravity anomaly maps show how much the Earth's actual gravity field differs from the gravity field of a uniform, featureless Earth surface. The anomalies highlight variations in the strength of the gravitational force over the surface of the Earth.