Maps of L1498, L1512, L1517BC, and L1400K showing positions where the radial velocity differences, ΔV, between the HC₃N (2–1) 18.196 GHz line and the NH₃ (1, 1) 23.694 GHz line have been measured at the Effelsberg 100-m radio telescope. On each panel the numbers are the mean velocity shifts ΔV (in m s^-1) between the corresponding ΔV_s and ΔV_a values listed in Tables 2–5. The circles show the half-power beam width at 23 GHz, whereas the linear scale is indicated by the horizontal bars. Reference positions are given in Table 1.