This scatter plot matrix uses D3 v5 to visualize the classic Iris dataset, comparing four flower measurements across all pairwise combinations. The matrix diagonal displays histograms of each feature, while the off-diagonal cells show colored scatter plots where each data point is colored red, blue, or green according to its species. The visualization uses `d3.scaleLinear` for the axes, `d3.scaleOrdinal` for the categorical color mapping, `d3.axisBottom` and `d3.axisLeft` for tick marks, and `d3.histogram` to compute the distribution bins.