  Using a grid of empirically calibrated synthetic spectra developed in our
previous study, we construct an all-sky 3D extinction map from the large
collection of low-resolution XP spectra in Gaia DR3. Along each line of sight,
with an area ranging from $0.2$ to $13.4$ deg$^2$, we determine both the
reddening and metallicity of main-sequence stars and model the foreground
extinction up to approximately $3$ kpc from the Sun. Furthermore, we explore
variations in the total-to-selective extinction ratio in our parameter search
and identify its mean systematic change across diverse cloud environments in
both hemispheres. In regions outside the densest parts of the clouds, our
reddening estimates are validated through comparisons with previous reddening
maps. However, a notable discrepancy arises in comparison to other independent
work based on XP spectra, which can be attributed to systematic offsets in
their metallicity estimates. On the other hand, our metallicity scale exhibits
reasonable agreement with the high-resolution spectroscopic abundance scale. We
also assess the accuracy of the XP spectra by applying our calibrated models,
and we confirm an increasing trend of flux overestimation at shorter
wavelengths below $400$ nm.
