Comparison between the inner widths () measured onthe high-resolution column density map (Fig. 3) and the FWHM fitted on the associated fibres seen in N₂H⁺. Each point is located at the average of the values measured eastwards and westwards of the crest vs. the median value of the fibre’s distribution of FWHMs. The error bars indicate the full range of values on both axes. The dotted red line shows the position of a linear fit to the data.