This example visualizes Bitcoin transaction data as an adjacency matrix, where each cell represents the connection weight between two nodes. The SVG rendering uses colored rectangles—darker blue indicates higher transaction weights, while gray represents no connection, with logarithmic scaling applied to the color intensity. The code loads CSV data via `d3.csv`, builds a symmetric matrix for the undirected graph, and renders rows and columns using D3 data joins. Hovering a cell triggers a CSS transition that scales and highlights it, and node labels appear along both axes. The implementation relies on D3 v7 selection methods and SVG transformations, with no external layout algorithms.