This line chart visualizes the unemployment rates of multiple U.S. metropolitan areas over time, with each area represented by a colored line. The chart uses D3.js APIs such as `scaleTime`, `scaleLinear`, `line` with `curveBasis`, and `axisBottom`/`axisLeft`, and it renders SVG elements. The data is sourced from a static `data.js` file, and the axis labels are localized in Chinese using `timeFormatLocale`.