This example visualizes the starting point of every arc in a TopoJSON file of U.S. state boundaries, rendered as a black dot on a mesh of state outlines. It loads the topology from `us.json` and uses `d3.geo.path()` with a `null` projection to draw the mesh. The code then plots each arc's start coordinate as a small circle, applying a custom `transform` function to map the TopoJSON coordinates using the file's `transform.scale` and `transform.translate` values. The visualization highlights how polygon boundaries are decomposed into shared arcs, revealing the topology's underlying structure.