US researchers have mapped the spatial organization of the human genome at an unprecedentedly high resolution of 1 kb using in situ Hi-C, an updated Hi-C methodology that enables DNA proximity ligation in intact nuclei. This approach yielded maps comprising 5 Tb of sequence data, with more than 15 billion distinct contacts recorded, which is an order of magnitude greater than all previously published Hi-C data sets combined. The maps reveal conserved contact domains and the existence of ~10,000 chromatin loops, which often demarcate these contact domains. A great majority of loops were found to be anchored at a pair of convergent CTCF binding sites.