SOM map projected on a plane formed by the two largest PCA vectors. Dots represent SOM neurons while lines are connections between neighboring neurons. The evolution of the SOM map projection during training is available as an online movie ‘fig_s5_som_pca12_movie’. One can see how the map goes from its starting position as a rectangle, changes during rough training (1–80 epoch), and converges to its final position during fine training (81–160 epoch).