The shape of the Earth is best described as an oblate spheroid. This means that it is roughly spherical, but slightly flattened at the poles and bulging at the equator. It is not a perfect sphere due to the Earth's rotation, which causes a centrifugal force that pushes the equatorial regions outward.
The Earth's shape was determined through various scientific measurements and observations. One of the earliest indications came from ancient Greek philosophers like Pythagoras and later Aristotle, who noted the curvature of the Earth's shadow during lunar eclipses.
Modern measurements and calculations, such as those performed by geodesists and surveyors, have provided more precise details about the Earth's shape. Satellite measurements, gravity data, and advanced technologies like global positioning systems (GPS) have further refined our understanding.
It is important to note that on a global scale, the Earth's surface has variations and irregularities, such as mountains, valleys, and oceanic features. These variations are relatively small compared to the overall size of the Earth and can be represented on maps and models.