A treemap visualizes the hierarchical structure of the Flare data set, with nested rectangles representing leaves sized by their numeric value. The visualization renders using SVG elements and includes an animated transition between two aggregation modes: "Size" and "Count". Built with D3 v4, the code uses `d3.treemap` with the `d3.treemapResquarify` tiling algorithm, `d3.hierarchy`, `d3.scaleOrdinal` for color, and `d3.interpolateRgb` for fading. A 2-second timer automatically triggers the mode change.