Star formation efficiency per gravitational free-fall time in 1.5 kpc regions. Each hexagonal point shows the integrated molecular gas depletion time for a 1.5 kpc diameter region as a function of the mass-weighted average τ_ff (see Eq. (4)) for 90 pc resolution clouds in that region. A straight, diagonal line in this space, such as the dark red one, corresponds to a fixed ϵ_ff, which could be expected if density variations represent the primary drivers of depletion time variations. We color the regions by galactocentric radius and calculate the implied ϵ_ff for each region. We estimate a median ϵ_ff of 0.45% with a 16 − 84% range of 0.33 − 0.71%, and we illustrate these with the solid red line and shaded pink region. For the central 1.5 kpc region, we illustrate the effect of switching from our adopted Galactic α_CO to a starburst conversion factor. The black cross shows a representative error bar as explained in the main text. The plotted values can be found in Table A.3.