This heatmap displays pairwise Pearson correlations among 18 numeric columns from the World Happiness Report 2021 dataset, using a diverging color scale from blue (negative) to red (positive) via `d3.scaleDiverging` and `d3.interpolateRdBu`. Each cell represents the correlation between two variables, with tooltips revealing exact r values. The code loads CSV data with `d3.csv`, computes correlations pairwise while ignoring missing values, and renders an SVG matrix with `d3.scaleBand` for axes and positioning.