  A comprehensive analysis of 355 high-quality WSRT HI 21-cm line maps of
nearby galaxies shows that the properties and incident rate of Damped
Lyman-alpha (DLA) absorption systems observed in the spectra of high redshift
QSOs are in good agreement with DLAs originating in gas disks of galaxies like
those in the z~0 population. Comparison of low-z DLA statistics with the HI
incidence rate and column density distribution f(N) for the local galaxy sample
shows no evidence for evolution in the integral "cross section density" below
z~1.5, implying that there is no need for a hidden population of galaxies or HI
clouds to contribute significantly to the DLA cross section. Compared with z~4,
our data indicates evolution of a factor of two in the comoving density along a
line of sight. We find that dN/dz(z=0)=0.045 +/- 0.006. The idea that the local
galaxy population can explain the DLAs is further strengthened by comparing the
properties of DLAs and DLA galaxies with the expectations based on our analysis
of local galaxies. The distribution of luminosities of DLA host galaxies, and
of impact parameters between QSOs and the centres of DLA galaxies, are in good
agreement with what is expected from local galaxies. Approximately 87% of low z
DLA galaxies are expected to be fainter than L* and 37 per cent have impact
parameters less than 1'' at z=0.5. The analysis shows that some host galaxies
with very low impact parameters and low luminosities are expected to be missed
in optical follow up surveys. The well-known metallicity-luminosity relation in
galaxies, in combination with metallicity gradients in galaxy disks, cause the
expected median metallicity of low redshift DLAs to be low (~1/7 solar), which
is also in good agreement with observations of low z DLAs. (Abridged)
