Procedure for finding the correct initialisation of the vertical profile. Top panel: initial (dashed lines) and final (solid lines) vertical metallicity profiles of the mock galaxy. The green line marks the model with the lowest final χ², while the blue and violet lines correspond to 1σ-worse models. The black line shows the vertical profile of the original mock galaxy. Bottom panel: map of final Δχ² as a function of initial G and N in Eq. (5). Grey crosses indicate the actually computed models, while the underlying coloured map is a result of interpolation. Red contours depict 1-, 2-, and 3-σ regions. The red cross indicates the model with the lowest χ².