Everything isp population based - incorporates large number of cells and you look for enrichment - more red, more enriched than you"d expect. Your"e only seeing significant red along diagonal - so chromosomes like interaction with themselves thna they like interacting with themselves. Some red off diagonal in cancer cell lines can appear. Fluid definitions or for better or for worse defines features found in hic. Zooming into higher resolution you get tads (topologically associated domains) - triangles along diagonals - enrichment of chromosome interactions, more zoomed in view than compartmnets. Sometimes within tads there are enrichment as corners -> chromatin loops. Boundaries between tads havei insulating activity and we know that there"s an insulator binding protein at ctcf regions. Tads are well conserved - many ctcf sites are conserved across cell types. Even break points are conserved across different species. Even though there are specific cell types - many are shared.