This example visualizes H1B petition case statuses across U.S. cities on a map using React and d3.v5. The map renders state boundaries and graticules with `d3.geoPath` and `d3.geoAlbers`, while city coordinates are projected from a CSV dataset containing longitude and latitude values. An interactive legend, built as a custom React component, uses `onMouseEnter` and `onMouseOut` handlers to highlight a selected case status by fading non-matching circles. The visualization loads geographic data from the us-atlas TopoJSON CDN and petition data from a GitHub-hosted CSV file.