R_D(DCO⁺) with column density, where in gray are all the pixels measured in DR21, purple is R_D(DCO⁺) where N(HCO)/N(H¹³CO⁺) was measured, orange is where X(SiO) was measured, and green is where N(HCO)/N(H¹³CO⁺) and X(SiO) intersect. The linear fit, where SiO and HCO are detected, is shown in dashed brown. The red and blue stars mark the surroundings of DR21 Main and DR21(OH), respectively.