This interactive scatter plot matrix visualizes the Iris dataset, showing pairwise relationships between sepal and petal measurements. Each cell displays the correlation between two features, with points colored by species. Users can brush a region in any plot to highlight the selected data points across all other cells simultaneously. The visualization uses D3 v4 with `d3.brush()` for selection, `d3.scaleLinear()` and `d3.axisBottom()`/`d3.axisLeft()` for axes, and `d3.scaleOrdinal()` for species coloring. Data is loaded from an external CSV file and rendered as SVG circles.