This chart uses an area mark with a monotone interpolation to display total billing amounts over the course of a year, with distinct areas for each year overlaid at partial opacity. The data is loaded from a remote CSV via D3’s `csv` function, filtered to exclude zero and large billing amounts, and aggregated by month and year. The visualization is built with the Vega-Lite API, encoding the month on the x-axis, total billing amount on the y-axis, and year as a color grouping, while enabling tooltips to inspect specific values.