extinction law is approximately flat between 4.5 and 8.0 , and therefore the contamination by extinguished field stars in this selection is reduced compared to other red-color criteria. By applying this condition to the entire GLIMPSE catalog, 268513 sources were selected. We did not impose the additional brightness and quality restrictions used by @Robitaille2008 because we favor the number of sources (and therefore higher sensitivity to possible YSO overdensities) rather than strict completeness and photometric reliability, which are not needed to only detect the locations of potential ECs. With the 268513 selected sources, a stellar surface density map was constructed by counting the number of sources within boxes of 0.01$\degr$ ($=36\arcsec$), in steps of 0.002$\degr$ ($=7.2\arcsec$). This significant oversampling was adopted in order to detect density enhancements that would have fallen into two or more boxes if we had used not overlapping bins. The bin size correspond to the typical angular dimension of some ECs serendipitously found using the on-line GLIMPSE viewer. To account for larger overdensities, a second stellar density map was produced with a bin size of 0.018$\degr$ ($=64.8\arcsec$), using the same step size of 0.002$\degr$.

The red-source density maps were checked in a test field, and we 