Illustrative method for computing the fractal dimension of a coronal hole using the box-counting method. (a) A binary map obtained from the synthetic image in Figure 4(d). The map is overlaid with square boxes of varying size w. The number of boxes that contain part of the boundary N(w) is counted, such as for (b) w = 8 and (c) w = 4. The fractal dimension is the negative slope of ﹩\mathrm{ln}(N(w))﹩ against ﹩\mathrm{ln}(w)﹩.