This interactive scatter plot matrix visualizes the classic Iris dataset, showing pairwise relationships between sepal length, sepal width, petal length, and petal width. Using D3 v6 with an SVG rendering, the scatter plot matrix uses `d3.scaleLinear` for axes, `d3.scaleOrdinal` for coloring the three Iris species, and `d3.brush` for interactive selection. Brushing on any scatter plot highlights that data subset across the entire matrix by dimming unselected circles, and a legend updates to indicate which species are currently included in the selection.