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Fig. 5.10. Fourier spectrum and gradient of the orientation map. (a) The Fourier spectrum is ring shaped as it is for biological maps (cf. Figure 5.1a), indicating that all directions are represented at regular intervals. (b) The global arrangement of high- and low-gradient areas is similar to that in biological maps: Regions with high gradient coincide with discontinuities such as pinwheel centers and fractures, and the fractures tend to connect the pinwheel centers (cf. Figure 5.1b).