  We investigate the oxygen and nitrogen abundance distributions across the
optical disks of 130 nearby late-type galaxies using around 3740 published
spectra of HII regions. We use these data in order to provide homogeneous
abundance determinations for all objects in the sample, including HII regions
in which not all of the usual diagnostic lines were measured. Examining the
relation between N and O abundances in these galaxies we find that the
abundances in their centres and at their isophotal R_25 disk radii follow the
same relation. The variation in N/H at a given O/H is around 0.3 dex. We
suggest that the observed spread in N/H may be partly caused by the time delay
between N and O enrichment and the different star formation histories in
galaxies of different morphological types and dimensions. We study the
correlations between the abundance properties (central O and N abundances,
radial O and N gradients) of a galaxy and its morphological type and dimension.
