Velocity (moment 1) maps overlaid with the intensity contours of the same line showing the velocity gradients in each clump. The top color bar is in units of km s⁻¹. Contour levels are shown on each image. All the velocity maps are generated with 3σ level of the average rms of HCO⁺ and N₂H⁺ channel maps. We show only a few examples here; maps for all the sources can be found in Fig. A.1.