  3D tomography of the interstellar dust and gas may be useful in many
respects, from the physical and chemical evolution of the ISM itself to
foreground decontamination of the CMB, or various studies of the environments
of specific objects. Our goal here is to bring more precise information on the
distance to nearby interstellar dust and gas clouds within 250 pc.
  We apply the best available calibration methods to a carefully screened set
of stellar Stromgren photometry data for targets possessing a Hipparcos
parallax and spectral type classification. We combine the derived interstellar
extinctions and the parallax distances for about 6,000 stars to build a 3D
tomography of the local dust. We use an inversion method based on a regularized
Bayesian approach and a least squares criterion. We obtain 3D maps of the
opacity and the distance to the main dust-bearing clouds with 250 pc.
  We calculate the integrated extinction between the Sun and the cube boundary
and compare with the total galactic extinction derived from infrared 2D maps.
We also compare the opacity distribution with the 3D distribution of
interstellar neutral sodium resulting from the inversion of sodium columns
towards about 1,700 target stars. Our maps show a larger high latitude dust
opacity in the North compared to the South, while gas maps do not show the same
asymmetry, suggesting a polar asymmetry of the dust to gas ratio at small
distances.
