United Kingdom Infra-Red Telescope (UKIRT) Wide Field Camera (WFCAM) continuum image of the DR21 Main region at 2.2 μm (Warren et al. 2007) and the line emission in key gas tracers observed as part of CASCADE. Shock-excited H₂ emission makes a significant contribution to the 2.2 μm image, in particular to the lobes off the central region. White contours mark the 5σ HCO⁺ (left), N₂H⁺ (middle), and SiO (right) emission. Intensities are integrated between −50 and 50, −20 and 10, and −20 and 20 km s⁻¹ for the HCO⁺, N₂H⁺, and SiO emission, respectively. The adopted point of origin of the outflow is marked in all cases with a red cross. Red dashed lines (middle) mark the three separate areas of the DR21 Main region used to extract the spectra in Fig. 2, with “E” marking the eastern outflow lobe, “C” the central area, and “W” the western outflow lobe. The magenta dashed box (right) marks the location of the interaction region shown in Fig. 11. Finally orange contours (right) show the 5σ integrated intensity of H41α from −30 to 30 km s⁻¹.