g varies due to Earth's shape, rotation, and position:

With Height (h above surface): Exact: $g_h$ = gR^$\frac{2}{R+h}$^2. This is an inverse-square drop. Approximation: $g_h$ ≈ g(1-2h/R) valid only for h << R. At h = R: g = g/4 $\frac{not g}{2}$. At h = 2R: g = g/9.

With Depth (d below surface): $g_d$ = g(1-d/R) — linear decrease assuming uniform density. At centre (d = R): g = 0. This is exact for uniform density.

With Latitude: $g_{eff}$ = g - R*$omega^2$*$cos^2$(lambda). Maximum at poles (cos90 = 0), minimum at equator (cos0 = 1). The difference is only 0.034 m/$s^2$.

Key comparison: For the same small deviation from the surface, g decreases faster with height $\frac{factor 2h}{R}$ than with depth $\frac{factor d}{R}$. This means d = 2h gives the same g value.