This brushable scatter plot matrix displays the classic Iris dataset, showing relationships among sepal and petal measurements for three flower species. Users can brush a rectangular region in any scatter plot to highlight corresponding data points across all other plots. The visualization uses D3 v4 with `d3.brush`, `d3.scaleLinear`, and `d3.axisBottom`/`d3.axisLeft` to render the SVG grid, with circle elements colored by species via `d3.scaleOrdinal`. Tooltips appear on hover, and selected points maintain their original colors while unselected points fade to gray.