Fraction of the observed [C ii] emission stemming from the cold neutral medium for T = 80 K and n = 100 cm^-3, after correction of the observed H i for the contribution from PDRs. Squares mark the individual data along the major axis. Their errorbars only include the 15% observational error of the H i intensities. Crosses in red mark the fractions averaged over the inner 2 kpc, the northern 2 to 4.5 kpc, and the outer, northern disk between 4.5 and 7.4 kpc. Corresponding errorbars show the standard deviation of the individual data and the radius interval over which the values were binned.