  We present absorption line strength maps of a sample of 24 representative
early-type spiral galaxies, mostly of type Sa, obtained as part of the SAURON
survey of nearby galaxies using our custom-built integral-field spectrograph.
Using high-quality spectra, spatially binned to a constant signal-to-noise, we
measure several key age, metallicity and abundance ratio sensitive indices from
the Lick/IDS system over a contiguous two-dimensional field including bulge and
inner disc. We present maps of H beta, Fe 5015 and Mg b, for each galaxy
  The absorption line maps show that many galaxies contain some younger
populations (<= 1 Gyr), distributed in small or large inner discs, or in
circumnuclear star forming rings. In many cases these young stars are formed in
circumnuclear mini-starbursts, which are dominating the light in the centres of
some of the early-type spirals. These mini-starburst cause a considerable
scatter in index-index diagrams such as Mg b- H beta and Mg b -Fe 5015, more
than is measured for early-type galaxies. We find that the central regions of
Sa galaxies display a wide range in ages, even within the galaxies. 50% of the
sample show velocity dispersion drops in their centres.
  All of the galaxies of our sample lie on or below the Mg b- $\sigma$ relation
for elliptical galaxies in the Coma cluster, and above the H beta absorption
line - $\sigma$ relation for elliptical galaxies. If those relations are
considered to be relations for the oldest local galaxies we see that our sample
of spirals has a considerable scatter in age, with the largest scatter at the
lowest $\sigma$. This is in disagreement with highly inclined samples, in which
generally only old stellar populations are found in the central regions.
  All this can be understood if ... (see paper for rest of abstract)
