  The HII regions are all studied employing the same general prescriptions,
despite the possible influence of their environment in their star formation
processes. Through the analysis of two samples of 725 inner and 671 outer disk
HII region observed spectra, we explore possible systematic differences between
their ionising clusters physical properties (metallicity, mass, and age),
comparing observations and predictions by photoionisation models. Higher
metallicities are confirmed for inner regions, although there are important
discrepancies between the diagnostic diagrams. Calibrations based on the N2
index may underestimate inner regions O/H due to the [NII] saturation at solar
metallicities. The degeneracy between the age and ionisation parameter affects
O/H calibrations based on the O3N2 index. Innermost regions have enhanced N/O
ratios, indicating an increase in the slope of the relation between N/O and
O/H. Ionisation parameter calibrations based on the [SII]/H{\alpha} ratio are
not valid for inner regions due to the bivalued behaviour of this ratio with
O/H. Innermost regions have lower [OII]/[OIII] ratios than expected, indicating
a possible non-linear relation between u and Z. Ionising and non-ionising
populations are present in both inner and outer regions. Inner regions show
larger ionising cluster masses that possibly compose star-forming complexes.
Outer regions might be affected by stochastic effects. Equivalent widths
indicate younger ages for outer regions, but degeneracy between evolution and
underlying population effects prevent a quantitative determination. Inner
regions have larger angular sizes, lower filling factors, and larger ionised
hydrogen masses. The confirmed systematic differences between ionising clusters
of inner and outer HII regions condition the validity and range of reliability
of O/H and u calibrations commonly applied to the study of HII regions.
