A scatter plot matrix of the Iris dataset displays pairwise relationships among four floral measurements, with histograms on the diagonal and color-coded points by species. Built with D3 v5, the visualization uses `d3.brush` for interactive selection, `d3.scaleOrdinal` for color mapping, and `d3.histogram` for density distributions. Axis labels are positioned via `d3.scalePoint`, and the layout adapts to the window size.