This pie chart visualizes the distribution of users across Android, iOS, and BlackBerry OS, aggregating yearly data from a CSV file into three slices with percentage labels. The code uses `d3.pie` and `d3.arc` to generate the SVG paths, `d3.scaleOrdinal` for color mapping, and `d3.csv` for data loading. Rounded corners on slices and a manual legend accompany the chart, while the title sits above the visualization.