Integrated intensities of selected molecules as a function of N′(H₂), which is the true model column density that has been scaled to take into account the density dependence of molecular abundances. Frame a shows the data for ideal observations (full model resolution) and frame b for the simulated ngVLA observations (resolution of ngVLA data). The contours are drawn at 10%, 50%, and 90% of the peak point density (pixels per logarithmic column-density and line-area interval). For HCO⁺ in frame a, the distribution is plotted also against N(H₂), showing the effect of lower average abundances at lower densities. For reference, the dashed black lines show two linear relationships that are separated by a factor of two along the W axis: W = 2 × 10⁻²² × N′(H₂) K km s⁻¹ and W = 4× 10⁻²² × N′(H₂) K kms⁻¹.