Comparison of the Planck (J = 1 → 0) Type 1 map to the NANTEN II survey in a 9° × 2° section of the Galactic plane. Top: combined NANTEN II map as ¹²CO + 0.53 × ¹³CO, where the factor applied to ¹³CO corresponds to the bandpass estimate of the ¹³CO contamination in the Type 1 map (see Sect. 6.2.2). Middle: Planck Type 1 J = 1 → 0 map. Bottom: correlation plot between the two maps. The colour scale represents the logarithm of the number of pixels in a given intensity bin. The solid and dashed lines represent perfect correlation (y = x) and the best linear fit, respectively. The best-fit slope and intercept are 1.007 ± 0.001 and 5.243 ± 0.032, respectively.