When global rotation stops, the massive oceanic water migration would cease and sea level would be at different locations, completely changing world geography. It is intermediate in the middle latitudes and weakest at the high altitudes of the Andes, close to the equator. The gravity of the still earth is the strongest at the polar regions (shown in green). The current difference between the average sea level as observed along the equator and the distance to the earth's center of mass from the sea level at the poles is about 21.4 kilometers (km). Consequently, the distance to the earth's center of mass is the longest around the equator and shortest beyond the polar circles. After a few billion years of spinning, the earth has taken on the shape of an ellipsoid (which can be thought of as a flattened sphere). Sea level is-and has always been-in equilibrium with the planet's gravity, which pulls the water toward the earth's center of mass, and the outward centrifugal force, which results from the earth's rotation. Why is the sea level where we currently observe it? What controls the sea level? How stable are the forces that determine the sea level? This article does not refer to the climate change and the potential increase of the water level in the global ocean but rather to the geometry of the globe and the powerful geophysical energies that determine where oceans lie.

It is zero elevation because it signifies the sea level. The line separating oceans from continents outlining the spatial extent of both land and water is the most fundamental contour. Typically, we do not pay much attention to the delineation of the sea because it seems so obvious and constant that we do not realize it is a foundation of geography and the basis for our perception of the physical world. The most significant feature on any map that depicts even a portion of the earth's ocean is the spatial extent of that water body. The flattening of the ellipsoid shown on this map was intentionally exaggerated. The longer, equatorial axis of Earth's ellipsoid is more than 21.4 km (or 1/3 of 1 percent) longer than the polar axis. The obvious demarcation of land and ocean is indicated by the contour of 0 elevation.

What does it mean to be down to earth