A force-directed network of cities and the routes between them. Nodes are colored by region and labeled with city names, while links visualize connections with line thickness scaled by route weight. Built with D3 v7, the layout uses `d3.forceSimulation` with forces for links, many-body repulsion, centering, and collision. Data is loaded from remote CSV files, and nodes can be dragged via `d3.drag`. The SVG rendering shows labels and tooltips on hover.