if you ask a average person about what is the shape of the earth?”,you will get a same type of answers ,some might say “it’s shaped lika a ball.”

others might say that the earth is “a sphere “or “an ellipsoid.”

but as an professional Gis Personal we can’t just say that we need some more precise answers with some mathematical model to understand the earth shape .

As early as the ancient Greeks, people understood the earth to be a sphere,but as centuries passed, scientists and explorers began to realise that the earth was not a perfect sphere.In the mid-18th century, a French survey expedition took measurements at the equator in Peru and at the Arctic circle in Lapland and determined that the earth was bulging at the equator.

The earth’s shape is not a sphere but rather an ellipsoid. Just as a sphere is based on a circle,

an ellipsoid is based on an ellipse.

By rotating an ellipse about one of its axes, an ellipsoid of rotation is created.

This type of ellipsoid most closely approximates the earth’s shape.

To be more precise, the earth rotates about its shortest axis, or minor axis,and is therefore described as an oblate ellipsoid.

Although the earth’s shape is technically an ellipsoid, its major and minor axes do not vary greatly.

In fact, its shape is so close to a sphere that it is often called a spheroid.The terms ellipsoid and spheroid are often used interchangeably and have caused confusion for many GIS users.Most map projection authorities consider both terms equally correct.By understanding the shape of the earth, and by using mathematical models to represent that shape,we are able to use GIS to map geographic information more accurately.

Shekhar Nath Chapagain

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