A line chart visualizes average salary against age, using aggregated employee data from a CSV file linked in the script. The D3.js code computes the mean salary for each distinct age value with `d3.rollups` and `d3.mean`, then sorts the results by age. The chart is rendered as an SVG, with axes created via `d3.axisBottom` and `d3.axisLeft`, and the trend line drawn using a `d3.line` generator. Points, a legend, and labels are added as SVG elements, with the chart's visual identity defined in the `styles.css` file.