Distribution of sources flagged as “secure Galactic” (red) and “secure extragalactic” (blue) in the g-r vs z-W1 (left) and W1 vs. X-ray (right) planes that were used to determine a line separator (black line) to classify sources in steps 5, 6, and 8 of the flowchart presented in Fig. 8. The line separator on the right has fewer Galactic sources that fall into the extragalactic locus. However, with the line separator defined on the left, only a handful of extragalactic sources fall into the Galactic locus. This makes this classifier more efficient when the four photometric points are available.