This bubble chart displays the relationship between average PM2.5 levels, average NO2 levels, and population across global cities. The visualization positions each city as a circle along x- and y-axes for the two air quality metrics, while circle size encodes population using d3.scaleSqrt. The chart draws SVG circles with d3.scaleOrdinal color mapping per city, and loads data from a GitHub-hosted CSV via d3.csv. Axes are generated with d3.axisBottom and d3.axisLeft, and the rendering includes labeled axes, stroke outlines, and 0.7 opacity for overlapping bubbles.