A multi-series chart combines bars for borrow counts and a line for average ratings across book genres, with ratings scaled by 100 to share a single axis. The visualization uses D3 v7 APIs including `d3.scaleBand`, `d3.scaleLinear`, `d3.rollups` for aggregation, and SVG rendering for both elements. Data comes from a CSV file containing genre, borrow count, and rating fields, processed with `d3.csv` and `d3.sum`/`d3.mean`. The chart includes axes, gridlines, and a legend distinguishing the two metrics.