• In the Milky Way, we can spatially resolve different gas components • We use large-scale surveys of 12CO and 13CO * Galactic Ring Survey (GRS, 13CO) * University of Massachusetts Stony Brook survey (UMSB) in 12CO * EXeter-FCRAO survey (EXFC) in 12CO and 13CO (outer Galaxy) * ThrUMMS survey (12CO and 13CO) * 45” beam • Follow a statistical method, no cloud decomposition • See Roman-Duval+2016 for details GRS + UMSB EXFC 55-100 EXFC 135-165 ThRUMMS New in 2017