Shape of the Earth

While everyone can witness and perceive that surface of the earth has an irregular and complicated shape, and it's a clear and definite fact, there are nevertheless many problems in modulating this irregular surface, as well as doing any kind of calculations in connection with it. For our practical applications, we need a regular and uniform shape that would be very close to the topographic surface of the earth. Remember that even the topography of the Himalayas Mountains, which are 8 kilometers high, appears as a thin layer in comparison to the 6400-kilometer radius of the earth; in other words, if it is shown in the global topography, it will have a radius of 2 meters, which means that its height cannot exceed 21.2 mm.