Excess Hα-band counts compared with the excess counts in the r_I band. Both quantities are the difference between the measured peak count and the estimated background level returned by HAGRID. It should be noted that the HAGRID output list is restricted to excess narrow-band counts > 10. The data are plotted as a density map and before any second-stage cleaning. The selection shown is from the sky region: (30° < ℓ < 95°, |b|< 4°). Working from top to bottom the red lines are: equality between counts (shown dashed), a line of slope 0.77 (solid) representative of nebula-dominated positions, and a line of slope 1/13 (solid) characteristic of star-like positions.