This heatmap shows the total wealth in billions for billionaires grouped by region and wealth type, with a tooltip revealing exact values on hover. The visualization uses D3 v6 to render an SVG grid where each rectangle’s fill color is mapped via `d3.scaleLinear` from white to steelblue. Axes are built with `d3.scaleBand` and `d3.axisBottom`/`d3.axisLeft`, while mouse events control the tooltip’s opacity and position. Data comes from the CORGIS Billionaires Dataset, pre-aggregated and loaded as CSV via `d3.csv`.