THOR+VGPS 1.4 GHz continuum map and H I integrated intensity map (− 113 < v_LSR < 163 km s⁻¹). The continuum map has a beam size of 25′′, and the beam size for the H I map is 40′′. In all panels, the circles mark the continuum sources that we used to extract the H I absorption spectra and construct the optical depth map (see Sect. 3.5.2). The Galactic sources are marked with white and black circles, and the extragalactic sources are marked with red circles. A few well-known Galactic sources are also labeled in each panel (W43 at l ~ 31°, W44 l ~ 35°, W49 l ~ 43° and W51 l ~ 49°).