We know that g=GM/R^2.
Mass of earth and G are both taken as constants.
so g is inversely related to R^2 (R=radius of earth)
1.So as R is more at equator g is less but vice verse in poles.
2.if we ascend to higher places then we will increase the distance from us to the center of earth so the new R'=R + the height attained by us, so again more R so g will be less .
3. if go underground also g is affected.