This visualization displays the Old Faithful dataset as a 2D heatmap using Vega-Lite’s binned rect marks, with a repeat operator to create a faceted grid of four plots comparing eruptions and waiting times. Users adjust bin counts via a MaxBins slider and brush a selection region to highlight outlier counts in green, while filtered bins render as grey. The tool uses d3.csv to load data, vegaEmbed to render the layered specification, and conditional color encodings tied to a brush parameter to reveal counts.