This heatmap visualizes earthquake occurrences across U.S. states by year, with color intensity representing the number of earthquakes per state-year combination. The x-axis is sorted by total earthquake count, while the y-axis orders years chronologically. Built with Vega-Lite and D3, it uses a `rect` mark with a red color scale and tooltips revealing exact values. Data comes from a CSV file fetched via D3’s `csv` function, then transformed from wide to long format before being passed to Vega-Lite’s encoding. The visualization is rendered as SVG with a custom configuration for improved readability.