"Harmonics are an invisible feature of locations which affect how sorcery is done. I can map them by watching them affect something simple," Promise makes a fairylight, "and in Fairyland I can typically cast reasonably well without doing that, but here the harmonics are thoroughly bizarre for some reason and I have to map an entire space grid by grid to be sure I can get a more complicated spell to go right." Pause. "It would also be interesting, if potentially disastrously complicated, if you turned out to be able to affect fairy orders, but those are not sorcery."