A D3.js scatter plot visualizes the Iris dataset, mapping petal length on the x-axis and sepal length on the y-axis as separate circles. The chart uses SVG rendering with `d3.scaleLinear` for both axes, `d3.extent` to compute domains, and `d3.axisLeft` and `d3.axisBottom` for tick marks. Data is loaded asynchronously from a CSV file via `d3.csv`, with petal width parsed as a numeric value. The visualization fills the browser window and sets a fixed circle radius of 5 pixels.