The Hα surface brightness - radius (SHα-r) relation is a robust distance indicator for planetary nebulae (PNe), further enhanced by different populations of PNe having distinct loci in SHα-r space. Other types of photoionized nebulae also plot in quite distinct regions in the SHa-r plane, allowing its use as a diagnostic tool. In particular, the nova shells and massive star ejecta (MSE) plot on relatively tight loci illustrating their evolutionary sequences. For the MSE, there is potential to develop a distance indicator for these objects, based on their trend in SHα-r space. As high-resolution, narrowband surveys of the nearest galaxies become more commonplace, the SHα-r plane is a potentially useful diagnostic tool to help identify the various ionized nebulae in these systems.