This visualization presents the classic Iris dataset as a scatterplot matrix, with each cell comparing two of the four measured features. The diagonal cells display histograms of each feature, while the off-diagonal cells show scatterplots of the data points. The code uses D3 v5 with SVG rendering, employing `d3.scaleLinear`, `d3.scalePoint`, and `d3.axisBottom`/`d3.axisLeft` to construct the axes. Each histogram is built with `d3.histogram`, and the points are colored by species using a custom color function. The visualization also includes a legend that allows users to select data subsets, which the histograms then update to reflect the filtered categories.