This example shows the spatial distribution of Airbnb listings across Chicago neighborhoods by overlaying red point markers onto a light blue choropleth map. A Mercator projection is created with `d3.geoMercator` and fitted to the map data using `fitSize`, while `d3.geoPath` renders the GeoJSON neighborhood boundaries. The listings are loaded from a CSV file and plotted as SVG circles, with their positions computed via the projection function. The visualization uses D3 v6 and relies on `Promise.all` to load both the GeoJSON and CSV data concurrently.