Spatial distributions of HC₃N v₇ = 1 emission in 20 sources associated with UC HII regions. The background images are moment-0 maps of v₇ = 1 emission. The white contours represent the intensity of continuum emission, with contour levels ranging from 10% to 90% of the peak values in steps of 20%. The red contours represent the intensity of UC HII regions (traced by H40α emission), also with contour levels ranging from 10% to 90% of the peak values in steps of 20%. The corresponding beam sizes are shown in the bottom left corner, and the linear scales are shown in the bottom right corner of the image of each source.