Top: slice of the ATLASGAL survey showing the active star-forming region, W51, which contains both diffuse emission and compact sources. Color scale starts at a 0.1 Jy/beam and goes to 40 Jy/beam. Dark gray contours start from 3σ level (0.21 Jy/beam) and continue show 10σ, 20σ, 40σ, 80σ, 160σ, 320σ, and 500σ. Green circles show the position of the extracted sources. A zoom towards the brightest continuum sources is shown in the inset, also known as W51 Main. Bottom: the same region as in the top panel but with emission larger than 100′′ scale removed.