This example shows monthly book purchase amounts as a force-directed node layout, where each circle’s size and color encode spending (green for ≤800, yellow for ≤900, orange for ≤1000, red above), with date and dollar labels. It uses D3 v3’s `d3.layout.force` for physics simulation, `d3.json` to load local sample data (originally from a Heroku DataClips endpoint), and SVG for rendering. Nodes are draggable via `force.drag`, with tick updates repositioning them.