Left panel: M31 R_proj and LOS distance for various regions in the GSS, from photometric measurements of Conn et al. (2016) and Ogami et al. (2025). For Conn et al. (2016) GSS sub-fields, small black circles denote distances and metallicities inferred from the single highest peak of their PDF, black triangles for quantities inferred by taking into account a secondary peak in the PDF, and grey diamonds for the fields with low signal-to-noise and high contamination fraction. Ogami et al. (2025) data are shown as yellow triangles. In blue we show the surface number density of star particles in the model. Middle panel: Comparison of the GSS’s average metallicity values from Conn et al. (2016), Escala et al. (2020), D23 and Ogami et al. (2025) with the equivalent values predicted by the model (indicated by blue crosses), binned in ∼2 kpc bins for clarity. The error bars for the [M/H] estimated by Ogami et al. (2025) represent the 68% uncertainty. Ogami et al. (2025) estimate their total systematic error in the estimated MW distance to be ∼27 kpc. Error bars for the data of Conn et al. (2016) represent their 1σ (68.2 percent) uncertainties. Conn et al. (2016) assume a fixed age of 9 Gyr for the GSS, while Ogami et al. (2025) assume a fixed age of 13 Gyr. The critical assumption of constant age breaks down in the GSS part which is close to the M31 disc (see for example the age spread in the resolved stellar population in Bernard et al. 2015). Right panel: Comparison of the σ[Fe/H] for stars in the model with equivalent measurements from observed datasets of Conn et al. (2016), Escala et al. (2020), D23 and Ogami et al. (2025).