This visualization presents the Old Faithful eruption dataset as a binned heatmap using Vega-Lite and D3 v4. It displays geyser eruption durations and waiting times on x and y axes, with color intensity representing the count of observations per bin. The heatmap dynamically updates in response to mouse movement, adjusting the bin count based on the cursor’s horizontal position. The code builds a Vega-Lite specification programmatically and renders it via vegaEmbed, while d3.tsv loads the source data from a GitHub gist.