Spatially resolved studies of star-forming regions show that the assumption of spherical symmetry is not realistic in most cases, further complication is added by the gas being ionised by multiple non centrally located stars or star clusters.
Geometrical effects including spatial configuration of ionising sources affect the temperature and ionisation structure of these regions. I will present the results of our recent theoretical investigation of these effects which made use of 3D photoionisation models using the 3D Monte Carlo photoionisation code MOCASSIN with various spatial configurations and ionisation sources. In particular I will illustrate the behaviour of temperature fluctuations within the ionised region as well as that of metallicity indicators based on strong-line methods, that are often our only means to determine the metallicity of extragalactic star-forming regions.