Distance comparison between paired ATLASGAL and Hi-GAL sources (3528 sources). (a) Sources with velocity difference less than 5 km s⁻¹ and longitude outside ±12° around the center and anti center directions. (b) Same figure but identifying the sources placed at the tangent distance in ATLASGAL (in red), and the sources with velocity lower than 10 km s⁻¹ (in green). The red dash-dotted line is the y = x line.