This free-free emission map has been obtained using radio recombination lines
at 1.4 GHz along the Galactic plane, for 20° < l < 40° and |b| < 4°.
At the resolution of 14.8', the map has been derived from H Parkes All-Sky Survey (HIPASS)
and associated Zone of Avoidance (ZOA) survey (see http://adsabs.harvard.edu/abs/2012MNRAS.422.2429A).
Units of the map are Kelvin (brightness temperature).