For estimating FST19 and for assessing the performance of assignment, we combined individuals into geographic groupings with larger and more comparable sample sizes than the original ancestral origins. These groupings do not reflect discrete structure in the data, rather the practical need to create geographical groupings with reasonable sample sizes. The strategy was to create a 3 × 3 grid of regions across Europe, with a tenth region for far southeastern Europe (Supplementary Table 3).
