This example visualizes the classic Iris dataset as a scatter plot, showing sepal length against sepal width. Each data point is rendered as a distinct SVG symbol (triangle, cross, or star) and color-coded by species: red for setosa, orange for virginica, and blue for versicolor. The visualization also includes linear regression lines for each species, calculated using a custom `leastSquaresequation` function, to highlight trends within the groups. Built with D3 v4, the code uses `d3.scaleLinear`, `d3.symbol`, and `d3.axisBottom`/`d3.axisLeft` to construct axes and symbols, with data loaded from an external CSV file.