Question

variation in the value of g due to shape of the earth

Answer 1

value of 'g' varies as gravity changes

Answer 2

the answer is: acceleration due to gravity is directly proportional to radius .as the value of radius increases the acceleration too increases.
the earth is not sphere it's minor flattened at poles .
thus,
the radius of earth is more at equator and less at poles. so acceleration due to gravity is more at equator than at poles.