The Earth's true shape is an oblate spheroid, which means it's a sphere that's slightly flattened at the poles and bulging at the equator. This shape is determined by a combination of factors:

* Gravity: Gravity pulls all matter towards the center of the Earth. This force is strongest at the center and weakens as you move further away.

* Rotation: The Earth's rotation creates centrifugal force, which pushes outward from the axis of rotation. This force is strongest at the equator, where the Earth's rotation speed is highest.

* Earth's internal structure: The Earth is not homogeneous. It has a dense core, a less dense mantle, and a thin crust. The distribution of mass within the Earth contributes to the uneven distribution of gravity.

How these factors work together:

1. Gravity pulls all matter towards the center, creating a spherical shape.

2. Centrifugal force from rotation counteracts gravity at the equator, causing the Earth to bulge outward.

3. The uneven distribution of mass within the Earth causes variations in gravity, leading to slight flattening at the poles.

As a result of these factors, the Earth's shape is not perfectly spherical. It's a slightly flattened sphere with a diameter of about 12,756 km at the equator and 12,714 km at the poles. This difference in diameter is only about 0.3%, but it's significant enough to affect various aspects of Earth's behavior, including the flow of air and ocean currents.