This interactive heat map visualizes the Old Faithful geyser dataset, showing the relationship between eruption duration and waiting time through a grid of colored rectangles. Using Vega-Lite’s binned aggregation, each cell’s color encodes the mean waiting time for eruptions within that bin, with a greyscale heatmap color scheme. The visualization is rendered as SVG via `vegaEmbed`, with the bin count dynamically adjusted based on mouse X position, triggering a re-render through the `d3.select` mousemove handler. Data is loaded from a TSV file using `d3.tsv`.