This area chart shows the number of iPhone users per year, with a smoothed line and a filled area beneath it to emphasize the trend. The visualization is rendered as an SVG using D3 v5, and relies on the `d3` API to load and parse CSV data from a remote gist. It constructs linear scales for both axes, and uses `line`, `area`, and `curveBasis` to generate the chart’s paths, with custom tick formatting for the y-axis.