This example visualizes the Old Faithful dataset as a 2D heatmap using Vega-Lite’s faceting, repeating columns and rows for each binned variable pair. It includes a brush interval parameter that filters a second layer of counts, highlighting only the brushed region’s outliers in a green scale, while unselected bins remain grey. The code uses vegaEmbed, vega-lite, and d3.csv to load the remote cardio_out.csv, with a MaxBins slider controlling histogram resolution.