 Local topography deviates from this idealized spheroid , although on a global scale these deviations are small compared to Earth 's radius : The maximum deviation of only 0 @.@ 17 % is at the Mariana Trench ( 10 @,@ 911 metres ( 35 @,@ 797 ft ) below local sea level ) , whereas Mount Everest ( 8 @,@ 848 metres ( 29 @,@ 029 ft ) above local sea level ) represents a deviation of 0 @.@ 14 % . If Earth were shrunk to the size of a billiard ball , some areas of Earth such as large mountain ranges and oceanic trenches would feel like tiny imperfections , whereas much of the planet , including the Great Plains and the abyssal plains , would feel smoother . 
