A multiple line chart displays temperature readings for several cities over a week, using the city as a color grouping. Each line is drawn with D3’s `line` generator, a basis curve, and a 5-pixel stroke, with a color legend built by a custom `colorLegend` function. Data comes from a CSV loaded via `d3.csv`, parsed into dates and numbers, and scales are set with `scaleTime`, `scaleLinear`, and `scaleOrdinal` from D3 v6.