Lets make a map
An interactive choropleth of South Korea lets users click any district to see its vote distribution rendered as a pie chart. The map is drawn with `d3.geoPath` and a Mercator projection, while district names come from a CSV mapped by `SIG_CD`. Clicking a city triggers a pie chart built with `d3.pie` and `d3.arc`, populating a second SVG. The visualization relies on TopoJSON for district boundaries, D3’s `select`, `csv`, and `json` loaders, and encodes vote counts from a separate CSV file.