Fig. 2From: Merging citizen science with epidemiology: design of a prospective feasibility study of health events and air pollution in Cologne, GermanyCologne Metropolitan Area with 100-m hexagon radius showing the number of inhabitants per hexagon. Data from https://dataforgood.fb.com/docs/high-resolution-population-density-maps-demographic-estimates-documentation/#datasets downloaded on 2021/04/18 Back to article page