This interactive scatterplot matrix visualizes the Iris dataset, displaying pairwise relationships between sepal and petal measurements across all combinations. Each off-diagonal cell shows a scatterplot of points colored by species, while diagonal cells display histograms of individual variables. Users can brush selections within any scatterplot cell to highlight corresponding points across all other cells simultaneously, with brushed points remaining visible while others fade to gray. The visualization uses D3 v7 with SVG rendering, employing `d3.brush()` for interactive selection, `d3.scaleLinear()` for axes, and `d3.bin()` to generate histograms.