Sample paths of pseudo-particles in the Galactic magnetic spiral field, colored by three different colors for three particles, each starting at the same point in phase space (i.e. Earth’s position at 1 GeV) and projected onto the Galactic plane. The black lines show integrated magnetic field lines to illustrate the magnetic field orientation. The left panel shows sample paths for isotropic diffusion, with no visible effect of the magnetic field orientation. The right panel illustrates the preferential diffusion along the magnetic field for a simulation with anisotropy ϵ = 0.1. Note that the exit point of the red particle in the right panel is actually the radial boundary, while the other particles all exit through the halo’s z-boundary (not visible).