Left: surface density of the infrared-excess-selected cYSOs resulting from the nearest neighbor analysis. The black dots represent the individual 8781 cYSOs. The locations of the main clusters like Tr 14, Tr 15, Tr 16, and NGC 3324 are easily visible. The black solid area is not covered by both surveys and therefore the density drops down to zero. The curvy border is a result of the contour smoothing. Right: contour representation of the surface density of the infrared-excess-selected cYSOs. The contours show surface density values from μ_min = 1044 deg^-2 (red) to μ_max = 23 640 deg^-2 (black), with the levels μ_k = (k/ 6)²·(μ_max−μ_min) + μ_min, with k = [0,6].