This visualization displays budget estimates for Block IV SSNs across fiscal years, using a line chart. Time-based axes for both year and delivery date plot data points from the "blockiv_ssn.csv" dataset. The code renders the chart with SVG, using `scaleTime` and `scaleOrdinal` for scaling, `axisBottom` and `axisLeft` for axes, and a custom `colorLegend` loop to differentiate SSNs by color. Lines are generated via `line` with `curveBasis`, and groups are sorted by descending last delivery year.