Radial variation of spectral indices. This plot portrays the latter four columns of Fig. 5 in a simpler fashion. The lines start with the median position of the inner regions (H II or GMC) and end at the median position of the outer regions. The marker near the line center indicates the median galactocentric distance of the whole sample, and column 5 of Tables 1 and 2 provides the correspondence with the optical radius R₂₅. Red lines are GMC indices and black lines show the indices of the HII regions. When the line goes up, the spectral index in the outer part is higher because the distribution is steeper (relatively more small objects).