Spectra extracted from individual 5 × 5 PACS spaxels at [N iii] 57.3 μm, [N ii] 121.9 μm, OH doublet 119.2/119.4 μm, and OH⁺ 153 μm in each of the two pointings toward NGC 6781 shown side by side: “center” on the right and “rim” on the left. To specify the instrument orientation, corner spaxels are identified by their identifiers. The flux unit is set to the surface brightness (mJy arcsec^-2). The background PACS 70 μm image indicates the approximate location of each spaxel. Ionic lines tend to be strong in the highly ionized cavity of the cylindrical structure, while atomic and molecular lines tend to be pronounced in the cylindrical rim of the nebula. Note that the footprint of the PACS IFU is not regular as implied by the placement of the subpanels; the slightly irregular footprint can be seen in Figs. 6 and 11.