Your weight changes depending on your location on Earth because gravity is not the same everywhere.

Earth is an oblate spheroid, meaning it bulges at the equator due to its rotation. This shape puts people at the equator further from the planet's center of mass than those at the poles. Consequently, gravity is about 0.5% weaker at the equator than at the poles. If you weigh 200 pounds at the North Pole, you would weigh about 199 pounds at the equator.In 2002, NASA and the German Aerospace Center launched the GRACE mission (Gravity Recovery and Climate Experiment). This mission used twin satellites to map Earth's gravity field with unprecedented precision. The data revealed 'gravity anomalies' caused by massive features like the Himalayas or deep-sea trenches. These variations are measured in units called 'gals' after Galileo Galilei.The distribution of water also plays a major role in these fluctuations. Melting glaciers and shifting ocean currents change the local mass of the planet over time. Scientists use this data to track climate change and sea-level rise. Even underground aquifers can influence the local gravitational pull as they fill or empty.These differences are so minute that humans cannot feel them without sensitive equipment. However, they are vital for calibrating high-precision scales and calculating satellite trajectories. Without accounting for these variations, GPS systems would lose accuracy over time. The most significant gravity low is found in the Indian Ocean, while highs are often found over tectonic plate boundaries.