This interactive scatter plot matrix visualizes the classic Iris flower dataset, showing the relationships between four morphological features across three species. Each off-diagonal panel displays a scatter plot of one feature pair, color-coded by species (red for setosa, blue for versicolor, green for virginica), while diagonal panels show histograms of individual feature distributions. The visualization uses D3 v5 with `d3.scaleLinear`, `d3.scaleOrdinal`, `d3.brush`, and `d3.histogram` APIs, rendering all elements as SVG. Users can brush within any scatter plot to select data points and filter the entire matrix, highlighting corresponding observations across all panels.