A sequential bar chart displays average horsepower for seven automobile brands, sorted from lowest to highest, with color intensity increasing alongside value. The visualization uses D3 v6 to construct SVG rectangles scaled by `d3.scaleBand` and `d3.scaleLinear`, while a `d3.scaleQuantize` maps horsepower values to a seven-step reds palette from colorbrewer. Hovering reveals a tooltip with the exact value, and an interactive legend and axes are generated using `d3.legendColor` and axis components. Data comes from a CSV file provided in the accompanying `barchart.csv`.