This example shows an adjacency matrix of Bitcoin transaction data, where each row and column represents a node and colored cells indicate weighted connections between them. The matrix is built by parsing a CSV file with d3.csv, creating a dense array of weights from the node pairs, and rendering it as an SVG grid of blue rectangles with opacity proportional to edge weight. The visualization uses D3 v7 for data binding and DOM manipulation, with a hover tooltip that displays the exact weight value via d3.select and transition. The animation-like interactivity comes from mouseover and mouseout events, while the white cell strokes and black hover outlines make the grid structure easy to read.