COSMOS Survey detections of emission-line galaxies with a blue continuum in the NB816 filter, which includes emission-line sources brighter than F = 10 ^−16.85 erg s ⁻¹ cm ⁻². Components of this sample are [O ii] emission at z ≈ 1.19, [O iii] at z ≈ 0.63, and Hα at z ≈ 0.25. The smaller circle is the IMACS field of our 2008 search; the larger circle, with a 0 70 radius, is the area we used for determining the foreground contamination per area. (This is most but not all of the rectangular area of the NB816 catalog.) Large-scale structure in the distribution of foreground galaxies can be clearly seen, particularly for the [O ii] emitters.