A pie chart visualization displays the distribution of cereals by manufacturer, using D3.js v7 to fetch and aggregate cereal data from a CSV file via `d3.csv` and `d3.rollups`. The pie slices are rendered as SVG paths with `d3.pie` and `d3.arc`, colored by a categorical scale, and labeled with manufacturer codes. A legend maps these codes to full manufacturer names, all presented in an SVG layout with a white background.