A force-directed network graph displays friendships among people in an example social network. Nodes are rendered as purple circles with labels, and directed links with arrowheads represent friend relationships. The code builds the visualization using `d3.forceSimulation` with link, charge, collision, and center forces. Nodes are draggable via `d3.drag`, and hovering applies a CSS class to change the stroke. The data comes from `data.json`, and the SVG is given a `viewBox` for scaling.