The data from the GOCE satellite reveals a potato-shaped earth defined by varying gravity. The globe seen below is a highly exaggerated rendering that neatly illustrates how the tug we feel from the mass of rock under our feet is not the same in every location. In fact, it varies widely. In this model gravity is strongest in yellow areas; it is weakest in blue ones.
The BBC says,
Technically speaking, the model is what researchers refer to as a geoid. It is not the easiest of concepts to grasp, but essentially it describes the “level” surface on an idealised world.
It is the shape the oceans would adopt if there were no winds, no currents and no tides. The differences have been magnified nearly 10,000 times to show up as they do in the new model.
Even so, a boat off the coast of Europe (bright yellow) can sit 180m “higher” than a boat in the middle of the Indian Ocean (deep blue) and still be on the same level plane. This is the trick gravity plays on Earth because the space rock on which we live is not a perfect sphere and its interior mass is not evenly distributed.