For the GPR model trained on the Ni data (Figure ), the substantial vertical spread of the 1st-6th NNs (colored, variable-size circles) are consistent with the fact that many points have distances on the order of 8-14°relative to the geodesic path between the two GBs. For perspective, these distances are greater than the global correlation length of 7.4°(Section 3.2.1), for which a higher proportion of distant points from the models are also distant crystallographically (small red and yellow circles). In other words, these trajectories traverse regions of the VFZ that are sparsely populated with data.