Fig. 2
From: Impact of air pollution on stunting among children in Africa
This figure conceptually demonstrates how environmental variables such as PM2.5 were joined with DHS sampling clusters. The blue point in the middle represents the sampling cluster. The red circle represents a 2 km urban area buffer around the cluster (note this is 5 km in rural areas). All environmental variables were averaged over the grid cells whose centroids fall within the red circle, which in this figure include cells E and F