The shape of the earth is roughly estimated as an oblate spheroid. This is because the earth is flattened at poles and bulges at the equator. The earth is quite oblong and slightly spherical; this is because of the rotation of the earth. When the earth rotates it has a tendency to bulge at the equator.
The earth is not a perfect oblate spheroid because mass is unevenly distributed within the planet. The greater the mass, the stronger the gravitational pull which creates bumps around the globe.
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