Two-dimensional histogram of the LOS (Z, Y) plane view of the M31 remnant. The centre of the galaxy is fixed at 773 kpc from the MW (Conn et al. 2016). All simulated particles [left], main progenitor particles [middle], and secondary progenitor particles [right] are plotted separately. The Z-axis of the simulation denotes our LOS and is designated as MW distance (our vantage point is marked on the bottom right of the leftmost panel). The Y-axis corresponds to the distance from the centre of M31 in the direction from north (up) to south (down) in units of kiloparsecs.