An interactive map of New York City's five boroughs displays traffic crash counts from a CSV dataset as circular markers with numeric labels, overlaid on a TopoJSON-derived GeoJSON map. Users hover over legend items or borough polygons to highlight matching regions while dimming others. The visualization uses React for component state and layout, D3 v7's `geoMercator` and `geoPath` for the map projection, and `select` for SVG updates. A semi-transparent legend communicates the fixed borough color scheme.