  A comprehensive investigation of logN-logS distributions of gamma-ray sources
discovered by EGRET has been performed for subsequent use in population
studies. Existing models explaining the spatial arrangement of unidentified
sources do not compare against an observed logN-logS distribution. However,
viable population models not only have to reproduce the logN-logS distribution
for different source classes globally, they have to correspond to apparent
differences among their spatial, spectral and variability characteristics.
Furthermore, it needs to be understood in which way results from selections
among the unidentified sources like "persistent" (Grenier 2000) or "steady"
sources (Gehrels et al. 2000) are related to the overall picture regarding
their logN-logS characteristics.
