Example of an asymmetry score map made using galaxies’ Lyα transmission. Left: Simulated ionization map (4 cMpc slice from our simulation with mean neutral fraction $\overline{x}=0.8$) and galaxies used to calculate asymmetry score. White regions are ionized, gray are neutral. The galaxies are color-coded by their modeled Lyα transmission, where we see galaxies with highest transmission are in the centers of bubbles. In the lower left corner we display a 10′ ruler (at z = 8) for gauging bubble size in angular scale. Middle: Asymmetry score map (red map). We plot the input ionization map (white contours) on top of the map. As expected, bubble edges have higher asymmetry score. Right: Asymmetry vector map where we see asymmetry vectors, color-coded by asymmetry score, point toward bubble edges, black contours mark the input ionization map.