A new methodology has been developed to study the fine details of GP zones in age-hardenable aluminium alloys. It is complementary to atomic resolution high-angle annular dark-field scanning transmission electron microscopy imaging, and combines scanning precession electron diffraction with diffraction simulations. To evaluate the method, data was collected from an Al-Zn-Mg alloy in a condition with a dense distribution of GPI zones. Diffraction patterns were recorded in the 〈001Al orientation, capturing GPI zones in three projections: along the unique GPI axis, and along the two other mutually orthogonal orientations. The GPI zones viewed along GPI revealed how the truncated octahedron units of the GPI zones were connected in multi-unit GP zones, while the two orientations normal to GPI highlight the internal structure. The stability of the atomic models developed based on the experimental results was verified by density functional theory calculations.