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A. A Brief Introduction to Map Projectio... > A.1. The Third Spheroid from the Sun

The Third Spheroid from the Sun

The Earth is round, or so they say. Video games, globes, and graphic art may depict the Earth as a perfect ball shape or sphere, but in reality the Earth is a bit squished. Therefore, we call the Earth a spheroid, rather than a sphere. It is sphere-like, but somewhat elliptical.

To take it one level further, we all know that the surface of the Earth isn’t perfectly uniform. There are mountains and valleys, bumps and dips. Geoid is the term used for a more detailed model of the Earth’s shape. At any point on the globe, the geoid may be higher or lower than the spheroid. Figure A-1 shows an example of the relationships among the sphere, spheroid, and geoid.


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