An Observable Plot starter demonstrates how to build an arrow variation chart, tracking changes in population and income inequality across U.S. metropolitan areas from 1980 to 2015. The `@observablehq/plot` library renders logarithmic x-axes, a color legend, and curved arrows whose stroke color encodes inequality shifts. It loads CSV data with `metros.csv`, converts strings to numbers, and dynamically sizes the plot to the container via `container.clientWidth` and `container.clientHeight`. The code includes hot-reloading support by replacing the container's first child on each run.