Why does gravity vary slightly at different places on Earth?

Gravity varies across Earth’s surface due to a combination of several physical factors. Because Earth is not a perfect sphere but rather an oblate spheroid that bulges at the Equator, the distance from the planet's center and the effects of centrifugal force change with latitude.12

The primary factors contributing to these variations include:

• Earth’s Shape and Rotation: The gravitational attraction of the planet as a whole and the centrifugal force generated by its rotation create a predictable variation in gravity based on latitude.2
• Elevation: Gravity decreases as one moves further from the center of the Earth, typically resulting in a reduction of approximately 0.3086 milligal per meter of elevation.2
• Local Density Variations: Irregularities in underground density distributions—such as salt domes, mineral deposits, or subterranean cavities—cause local gravity anomalies.32
• Topography: Surface features like mountains and valleys create unbalanced gravitational attractions that require corrections in geophysical surveys.32
• Tidal Variations: The gravitational influence of other celestial bodies causes small, periodic tidal fluctuations in gravity.2

These irregularities are why scientists use the geoid—a model representing mean sea level—to accurately map the Earth's gravitational field.41