This example visualizes a choropleth map of Yunnan Province, China, with selectable countries. The map encodes a categorical color value (`yszl`) using an ordinal color scale with a spectral scheme, and users can click individual countries to highlight them and dim the rest. A color legend allows filtering by color value. The visualization uses D3 v5’s `geoPath`, `geoMercator`, and `zoom` modules to project and render GeoJSON features, while the legend and map interactions are built with D3’s selection and event APIs. Data is loaded from external CSV and JSON sources.