H i and H₂ surface densities (red and blue curves plus triangles, respectively) and the H₂-to-H i ratio (black curve) measured throughout the W43 atomic/molecular cloud complex and the nearby clouds. Measurements are averaged within rectangular annuli centered at l = 30.5° and b = 0° and with an aspect ratio 3:2. The dashed vertical line outlines the extent of the W43 complex, the dotted vertical line and arrow locate the region inside which the H i line emission is widely optically thick. The H i surface density is significantly higher than the equilibrium models predict, while the H₂ density remains high, in disagreement with a clear H i/H₂ transition.