A heatmap displays a 10x10 matrix of values as colored squares, using a white-to-teal linear scale to represent the data range from 1 to 100. The visualization is rendered as an SVG chart using React components, D3.js scales (scaleBand, scaleLinear), and data loaded from a CSV file via d3.csv. Hovering over a square toggles its border and reveals the exact value in bold text, implemented through React's useState hook for interactive tooltips.