This example shows a multi-series chart comparing city population and density, with blue bars for population values and a red line for density. The visualization uses D3 v7 to load CSV data from a GitHub gist, then renders an SVG with dual y-axes: population on the left and density on the right. The code employs `d3.scaleBand` for the categorical x-axis, `d3.scaleLinear` for both y scales, and `d3.line` to generate the density path. Rotated axis labels and a manual legend distinguish the two metrics.