Left: map of the reddening corrected Hα line flux as described in Sect. 3.1. The position of HD 164492A is marked with a grey star, while the position of HD 164514 is marked with a white star. The extent of the measured Strömgren sphere (Sect. 3.4) is shown by a grey dashed circle. Right: radial variation of the reddening corrected Hα line flux as a function of the distance to the ionizing star HD 164492A. Faint points represent individual spaxels, while opaque points show the uncertainty-weighted average of all spaxels within 0.1 pc wide distance bins. Standard deviations are shown as error bars. The extent of the measured Strömgren sphere (Sect. 3.4) is shown by a grey dashed line together with the error as a grey shaded region.