Fig. 4: Distribution of participants (Notes: The population density in Northwestern China is relatively low, rather than gaps in coverage).
From: Sustainable development reduces particulate matter emissions and mitigates aging’s cognitive impact
Spatial distribution of survey participants across China. Colored circles represent the number of participants at each ___location, ranging from green (approximately 100 participants) to red (up to 500 participants). The sparse distribution of circles in northwest China reflects lower population density rather than insufficient survey coverage, supporting the representativeness of the sampling across regions.
