This area chart shows the average fuel efficiency (MPG) of cars by model year, using data from the auto-mpg.csv dataset. The code loads the CSV with d3.csv, filters out invalid entries, aggregates averages with d3.rollups, and renders a smooth, semi-transparent blue area using d3.area with curveMonotoneX. Axes are drawn with d3.axisBottom and d3.axisLeft, and the chart is built in SVG.