This area chart visualizes the average car horsepower by year, using data from a car performance CSV loaded via `d3.csv`. The chart aggregates raw Horsepower values into yearly averages with `d3.rollup`, then renders a semi-transparent filled area, an overlaid blue line, and interactive circles. It uses `d3.area`, `d3.line`, and `d3.scaleLinear` within an SVG, with a custom mouseover tooltip. The axes are labeled "Year" and "Horsepower," and the visualization is built entirely with D3.js v7.