(a) Stellar surface density/metallicity map of M31 from I07. The shallower INT/WFC survey is used inside the large ellipse, and the deeper CFHT/MegaCam survey outside it. The minor‐axis streams C and D are visible at the lower left, projecting from the larger plume of the GSS. These streams (green) and the GSS cocoon (red) are observed to be more metal‐poor than the GSS core (yellow). (b) Mass surface density map from disk A, 840 Myr into the run. The map is 160 kpc on a side, and a dotted contour indicates M31’s disk orientation. The square indicates the region shown in Fig. 2. (c) Same for disk B, at 680 Myr. (d) Same for the Plummer model, at 840 Myr. (e) Map of the metallicity as a function of position in disk A (at 840 Myr), with red denoting the highest metallicity, dark blue intermediate, and light blue the lowest (see Fig. 2b for a quantitative scale). Boxes show the regions used for the metallicity histograms in Fig. 2. (f) Same for disk B (at 680 Myr).