New criteria are presented for the classification and statistical analysis of defects from irradiation cascades that allow a more detailed description of the diversity of damage, especially amorphous regions. Classical molecular dynamics simulations are used to analyze the damage produced by 2 keV Si recoils annealed at 1000 K for 1 ns. Based on a density grouping criterion of elementary defects (displaced atoms and empty lattice sites) the non-uniformity of local defect density within damage regions is revealed. The density criterion is able to distinguish dense damage regions which evolve independently upon annealing (although they are connected by some defects), while keeping small and compact regions unaltered. Damage regions are classified according to the size, net number of defects and compactness, calculated by averaging the distance among all defects, parameters that have a direct impact on their stability.