This visualization presents a brushable scatter plot matrix of the classic Iris dataset, showing pairwise relationships between four floral measurements across 150 flowers. Users can brush points in any scatter plot pane to highlight selections, which are then reflected in all other panels and as color-coded, stacked histograms along the diagonal. The chart is built with D3 v7, using `d3.brush` for interactive selection, `d3.scalePoint` for panel positioning, and SVG elements for all rendering. Each flower is colored by its species using an ordinal scale, with unselected points rendered in black.