Robustness is a fundamental scientific concern in low-density geochemical mapping, which has long garnered close attention from mapping researchers. However, quantitative understanding of robustness has been lacking due to the lack of effective quantitative assessment methods. In this study, using cobalt element data from two low-density mapping sources—the China Geochemical Baselines project (CGB) and the Regional Geochemical National Reconnaissance project (RGNR)—robustness is quantitatively assessed based on 1546 representative catchments through the utilization of local spatial correlation coefficients; the spatial distribution features and influencing factors are also discussed. On a national scale, robustness was influenced by sediment cobalt (Co) content and geochemical landscape conditions; on a local scale, it was affected by differential erosion in cobalt-rich and Co-poor source areas. In Co-poor environments (sediment Co<13 μg/g) the robustness index (R) value fluctuated around 0.4, while in Co-rich environments (sediment Co>13 μg/g) it increased from 0.4 to above 0.6 with rising Co content. Regions such as karst terrains, tropical rainforests, and semi-arid low hills had R values as high as 0.58 to 0.74, whereas alluvial plains and forested swamp regions had R values below 0.32. This study provides a reference for quantitative evaluaton of low-density mapping, deomonstrating that low-density geochemical mapping has good robustness and promising prospect in the global-scale geochemical mapping.