This example visualizes the classic Iris dataset as a scatter plot, showing the relationship between petal length (x-axis) and sepal length (y-axis) for three flower species, with each species color-coded via a custom marker function. The plot uses D3.js v6 to load CSV data, parse numeric fields, and render SVG circles positioned with `d3.scaleLinear` and `d3.extent`. Axes are drawn using `d3.axisLeft` and `d3.axisBottom`, while labels are added manually. The implementation also leverages `d3.csv` for asynchronous data fetching and `select`/`join` for data binding, with a responsive full-window SVG layout.