Vertical distribution of molecular gas traced by CO as a function of Galactocentric radius, with the contributions of the diffuse extended (detected in ¹²CO but not ¹³CO) and dense (detected in ¹²CO and ¹³CO) components in red and green respectively. The vertical distributions are derived with the combined data sets. in the inner Galaxy, the very dense component traced by CS emission is shown in blue. The black lines corresponds to the total profiles.