This heatmap visualizes student grades across five subjects, encoding each value as a colored, rounded rectangle. Rendered as an SVG using D3.js v4, it employs `d3.scaleSequential` with an interpolateCool color scheme, `d3.axisBottom` and `d3.axisLeft` for categorical axes, and interactive tooltips triggered by mouse events. The data comes from a CSV file containing grades for ten students across five subjects.