This line chart visualizes simulated ILINet flu surveillance data, showing flu cases across US regions by week of the year, with each line colored by year. The visualization aggregates the data by year, region, and week before plotting. It uses the Vega-Lite API through the vega-lite-api library, with D3.js handling data loading from a CSV file. The custom config adjusts axis styling, font sizes, and colors for improved readability, while vega-tooltip provides interactive hover details.