NASA’s GRACE mission and other international efforts map Earth’s gravitational field to define the geoid—the planet’s actual, irregular shape rather than a perfect sphere.
Uneven mass inside Earth, including rocks, magma and water, alters gravity from place to place, creating stronger-pull “hills” and weaker-pull “valleys” in the geoid.
NASA illustrates those subtle variations with an exaggerated “dented potato” image, even though the real distortions are too small to see at human scale.
The geoid differs from the smoother ellipsoid used in calculations because it reflects how ocean water would settle at rest under Earth’s real gravity field.