examples/choropleth.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <title>US Choropleth Map</title>
    <meta name="description" content="force directed graph example" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js"></script>
    <script src="../web_modules/d3/dist/d3.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/topojson-client"></script>
    <link href="./style.css" rel="stylesheet" />
    <style>
      path {
        stroke: #999;
      }
      path:hover {
        stroke: black;
      }
    </style>
  </head>

  <body>
    <h1>US Choropleth Map</h1>

    <script>
      const margin = {
        top: 10,
        bottom: 10,
        left: 10,
        right: 10,
      };
      const width = 800 - margin.left - margin.right;
      const height = 600 - margin.top - margin.bottom;

      // Creates sources <svg> element and inner g (for margins)
      const svg = d3
        .select("body")
        .append("svg")
        .attr("width", width + margin.left + margin.right)
        .attr("height", height + margin.top + margin.bottom)
        .append("g")
        .attr("transform", `translate(${margin.left}, ${margin.top})`);

      /////////////////////////
      const projection = d3.geoAlbersUsa();
      const path = d3.geoPath(projection);
      const color = d3.scaleSequential(d3.interpolateBlues);

      d3.json("https://cdn.jsdelivr.net/npm/us-atlas/states-10m.json").then((us) => {
        const states = topojson.feature(us, us.objects.states).features;
        const nation = topojson.feature(us, us.objects.nation).features[0];

        // scale to fit bounds
        projection.fitSize([width, height], nation);

        const data = states.map((feature) => ({
          feature: feature,
          name: feature.properties.name,
          value: Math.random(), // random value
        }));

        const paths = svg
          .selectAll("path")
          .data(data)
          .join((enter) => {
            const p = enter.append("path");
            p.on("mouseenter", function () {
              // move the SVG element after all other elements to be on the top
              d3.select(this).raise();
            });
            p.append("title");
            return p;
          })
          .attr("d", (d) => path(d.feature))
          .style("fill", (d) => color(d.value));
        paths.select("title").text((d) => d.name);
      });
    </script>
  </body>
</html>