Upper row: 2D histograms of the correlations between the total gas column density, N_{H γ}, measured by the 10^2.6−5 MeV interstellar γ rays, and the dust tracers convolved with the LAT response for an interstellar spectrum. The maps were sampled on a 0.̊375 pixel grid. The solid lines mark the best linear regressions through the data points of the maps. Lower row: evolution of the dust properties per gas nucleon in bins of N_{H γ}. The error bars and shaded areas respectively give the standard error of the means and the standard deviations in each bin. The dashed lines give the mean ratios at low N_H, in the (1−2.2) × 10²¹ cm^-2 interval.