Why acceleration due to gravity (g) varies from place to place on earth.

Why acceleration due to gravity (g) varies from place to place on earth.

On the earth surface, g is inversely proportional to the radius of the earth. This means that as radius from center of earth  increases, acceleration due to gravity (g) decreases. 

The earth is not a perfect sphere. This implies that different places on the the earth are of different radius from the center of the earth.

Hence acceleration due to gravity varies from place to place.

Question: why is acceleration due to gravity (g) less at the mountain top? (Leave comment below).