Column density of H i and H₂ measured in elliptical annuli around W43 MM1. The x-axis presents the equivalent radius of these elliptical annuli. The black and green lines represent the fitted curves with the corresponding 1σ uncertainties shown as a gray shaded area. The larger symbols (diamonds for H₂, squares for H i) present the averaged value of the elliptical annuli and their corresponding variations within the annuli. As the optical depth spectra saturates, we can only determine lower limits for the H i column density. The blue dots and line show the H₂ and H i column density ratio of the data and the fitted curves, respectively.