Geometric cross sections of the resultant aggregates in the case of v _imp = 0.54 m s ⁻¹ and ξ _c = 2 Å as a function of the number of particles N. In panel (a), the dots show geometric cross sections for 30 directions, and the line shows the mean geometric cross section. In Panel (b), thin gray lines show mean geometric cross sections calculated for 30 resultant aggregates, and the solid line shows the average value of them. We obtain evolution of the geometric cross section with these two kinds of averaging.