ILINet Flu Surveillance Data
This line chart displays annual U.S. influenza-like illness (ILI) totals by week, with one colored curve per year from 2015 to 2019, enabling year-over-year comparison. The data originates from CDC FluView Interactive and is loaded via `d3.csv`. The visualization uses the Vega-Lite API (`vl.markLine`), aggregating `ILITOTAL` by year, region, and week with `vl.aggregate` and encoding year with an unordered color scale. A custom `config` adjusts axis and label styling for readability.