Quantification of the spatial associations between homeostatic HSCs and their BM niches. (A) Most imaging studies have quantified HSC localization in relation to individual BM niche population per sample (upper panel). BM niche populations are ranked based on the frequency of HSCs found in their immediate proximity (higher frequency at the top, green shape). To account for the relative abundance of displayed populations, the association frequency of average cells (usually calculated by random dots) is also shown (gray shape). For example, Cxcl12⁺/LepR⁺ MSCs are placed at the top, because >80% of both adult HSCs and average cells locate next to them due to the dense MSC network and tissue abundance. (B) Quantification of anatomical HSC association with multiple BM niche populations imaged simultaneously on the same sample is essential to unravel the complexity of the BM HSC niche (10 μm distance). NG2, chondroitin sulfate proteoglycan 4.