The characteristics of this widely used representation of Earth's surface

This projection is one of the most recognizable depictions of the Earth. It is nearly equivalent to viewing the surface of a globe from a spot high above the surface, and shows an entire hemisphere at a time. In the case of the Earth, the point on the surface nearest to the observer is called the nadir, an Arabic word meaning "lowest point," and is essentially located at the very center of the planet's disk. For very small areas near the nadir, the four characteristics of distortion - shape, area, distance, and direction - are almost negligible. However, moving away from the nadir (since the view of the surface is now at some angle), the general distortion becomes greater with increasing distance, until the very edge of the Earth is reached (called the limb), upon which features become unrecognizable. Despite the straightforward appearance of this projection, its use is limited to graphical representations, such as animations showing the spinning motion of the Earth rotating on its axis. The most practical purpose of this projection is its use as a map of the visible, Earth-facing side of the Moon. It is sometimes produced as a "polar projection" to show the Earth with the North or South Pole at the center.

Credit: Dylan Prentiss, Department of Geography, University of California, Santa Barbara

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