Source exclusion mask that has been applied in our analysis. Sources with coordinates within the shaded regions have been excluded from our analysis. The locations of sources in our samples are also indicated. Cross signs: Possible 3EG blazars (included in sample 1 only). Squares: Originally unidentified in 3EG, with later suggested associations (included in samples 1 and 2). Triangles: Sources included in all three samples (unidentified in 3EG, no counterpart suggested to this day).