Ratio of column density from radiative transfer computation to ¹³CO(2−1) integrated intensity, N/I, as a function of the same integrated intensity, for the ~140 000 voxels in the science demonstration field with I above a 5-σ level of 0.44 K  km s^-1. The red line shows the trend of median values (which are very similar to the means) for the data binned into ten equal log(I) intervals while the green lines show the 2-σ excursions from the median values.