GLIMPSE 8 µm map overlaid with blue contours of the radio emission at 1400 MHz at full resolution. The contour levels are as described in the left panel of Fig. 1. The black circles represent the HII regions toward W33 Main and G12.81−0.22 taken from the WISE catalog of Galactic HII regions (Anderson et al. 2014). Some regions have been slightly adjusted in order to avoid overlap and for better correlation with radio and 8 µm emission.