This is in part motivated by the discussion in astropy/astropy#733 . There was (and is) a discussion there about whether or not Galactic extinction should be included in the astropy core vs. astroquery.

Regardless of what goes in the core, it is clear that quite a few different online queryable source exist for all-sky or large-field dust maps, either in E(B-V) form or as dust columns or the like. Some possible examples include

• The online queryable for the SFD dustmaps at http://irsa.ipac.caltech.edu/applications/DUST/docs/dustProgramInterface.html
• The http://ogle.astrouw.edu.pl/cgi-ogle/getext.py interface to get E(B-V) near the galactic bulge
• Planck's maps - I don't think there's a dust map yet, but it's bound to show up at some point (at http://irsa.ipac.caltech.edu/Missions/planck.html ?)
• The LAB Survey neutral HI mentioned by @zblz in Tool to get SFD dustmap values astropy#733 -http://vizier.cfa.harvard.edu/viz-bin/Cat?VIII/76

So this issue calls for creating an interface that might allow various sources like this to be queried and return the same/similar type of object. That is, it would be really nice to be able to just do something like:

ebmv1 = query_ebmv(coordinates, 'SFD')
ebmv2 = query_ebmv(coordinates, 'ogle-vvv')

and have ebmv1 and ebmv2 be exactly comparable.

(of course it should match the general API plan for astroquery, but the result object should be something consistent across the disperate tools.)