Diagnostic graphs for six selected emission line spectra in SH2 (see Table 3 and Sect. 5.2 for explanation). These spectra are compared to Hii region models from Dopita et al. (2013) with the ionisation parameter log q and four oxygen abundances (0.5 × solar, solar, 2 × solar, and 3 × solar) as parameters. The solid lines are lines of constant oxygen abundance and varying log q. In the left panel, the range of log q values is indicated, and is the same for all panels. The models refer to κ = ∞ (corresponding to a Boltzmann electron distribution). The dotted lines in the middle and right panels separate Hii regions from AGN- and LINER-spectra according to Kewley et al. (2001). All spectra except 25:17 are consistent with a uniform abundance value, although [Oiii]/Hβ varies significantly. The middle and the right graph show the degeneracy for high metallicities that is not present in the left graph. A super-solar oxygen abundance is supported by all three diagnostic graphs.