Galactic distribution of the source sample. The locations of the targets are denoted by red stars on an artistic rendering of the Milky Way. The distances to the observed H II regions and their associated clumps are taken from Paper I (and references therein). The spiral arms are marked following the description presented in Reid et al. (2019), and the individual spiral arms are colored as follows: the 3 kpc in magenta, the Norma-Outer Arm in red, the Scutum-Centaurus Arm in blue, the Sagittarius-Carina Arm in green, the Local Arm in cyan, and the Perseus Arm is in yellow.