Synchrotron spectral index map of NGC 6946 overlaid with contours of the linearly polarized emission at 6 cm (top) tracing the ordered magnetic field in the sky plane with the same levels as in Fig. 3 and of bright Hα sources (bottom). The Hα contour levels are 18, 24, 35, and 47% of the maximum intensity. The 9 giant Hii regions are indicated (Table 4). The bars at the right of the images show the values of the synchrotron spectral index.