We know that earth is not a perfect sphere. So the value of R is not the same at all places.

So, the value of acceleration due to gravity g is not constant at all places on the surface of earth.

Where, G = Gravitational Constant

M = Mass of Earth

R = Radius of Earth

Since, G and M are constant, so g depends on the radius of earth.

So, from the above we can say that,

g

Now, radius of earth is minimum at poles. So, acceleration due to gravity is maximum at poles.

But radius at equator is maximum, so acceleration due to gravity is minimum at equator.