Top: profile of differential gas flow d²M/dR dt driven by gravitational torques across NGC 628. The inner corotation radius (CoR_in; shown by an arrow) is located where torques and gas flows cross from negative (inward) to positive (outward), as illustrated by the short-dashed segment. The second arrow marks the position of the outer corotation radius, CoR_out, previously identified by Cepa & Beckman (1990), which falls near the edge of the CO field of view. Middle: profile of integrated mass flow rates from the CoR_out inward to radius R. Net flows are radially inward (negative) at all radii. The uncertainty on the inflow (not shown) is dominated by the large, 15″ uncertainty in the position of the CoR_out near the map edge. Bottom: angular frequency curves in NGC 628, Ω (solid), Ω ± κ/2 (dashed) and Ω ± κ/4 (dotted). Positions of dynamical resonances and corotation radii are indicated. The hashed vertical bar highlights the overlap between the CoR_in and the outer ultra-harmonic resonance.