MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a 6-year SDSS-IV survey that will obtain spatially resolved spectroscopy from 3600 A to 10300 A for a representative sample of over 10000 nearby galaxies. In this paper we present the analysis of nebular emission line properties using observations of 14 galaxies obtained with P-MaNGA, a prototype of the MaNGA instrument. By using spatially resolved diagnostic diagrams we nd extended star formation in galaxies that are centrally dominated by Seyfert/LINER-like emission, which illustrates that galaxy characterisations based on single bre spectra are necessarily incomplete. We observe extended LINER-like emission (up to 1Re) in the central regions of three galaxies. We make use of the EW(H) to argue that the observed emission is consistent with ionisation from hot evolved stars. We derive stellar population indices and demonstrate a clear correlation between D n (4000) and EW(Hδ A ) and the position in the ionisation diagnostic diagram: resolved galactic regions which are ionised by a Seyfert/LINER-like radiation field are also devoid of recent star formation and host older and/or more metal rich stellar populations. We also detect extraplanar LINER-like emission in two highly inclined galaxies, and identify it with diuse ionised gas. We investigate spatially resolved metallicities and nd a positive correlation between metallicity and star formation rate (SFR) surface density. We further study the relation between N/O vs O/H on resolved scales. We find that, at given N/O, regions within individual galaxies are spread towards lower metallicities, deviating from the sequence dened by galactic central regions as traced by Sloan 300 bre spectra. We suggest that the observed dispersion can be a tracer for gas ows in galaxies: infalls of pristine gas and/or the effect of a galactic fountain.