{\bf Left} The scatter plot of column density estimates in units of equivalent V-band extinction, based on the 2MASS/NICER extinction and the Herschel data, with a varying spectral index $\beta$. {\bf Right} Regions corresponding to the three ``sub-populations'' identified on the plot of A$_V$-A$_V$. The regions are overlaid on the 2MASS extinction map in gray scale. The plots are made with Glue (Beaumont et al 2012; see \url{http://glueviz.org} for information about Glue).