Index: node_modules/d3-contour/src/density.js
===================================================================
--- node_modules/d3-contour/src/density.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/density.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,149 @@
+import {blur2, max, ticks} from "d3-array";
+import {slice} from "./array.js";
+import constant from "./constant.js";
+import Contours from "./contours.js";
+
+function defaultX(d) {
+  return d[0];
+}
+
+function defaultY(d) {
+  return d[1];
+}
+
+function defaultWeight() {
+  return 1;
+}
+
+export default function() {
+  var x = defaultX,
+      y = defaultY,
+      weight = defaultWeight,
+      dx = 960,
+      dy = 500,
+      r = 20, // blur radius
+      k = 2, // log2(grid cell size)
+      o = r * 3, // grid offset, to pad for blur
+      n = (dx + o * 2) >> k, // grid width
+      m = (dy + o * 2) >> k, // grid height
+      threshold = constant(20);
+
+  function grid(data) {
+    var values = new Float32Array(n * m),
+        pow2k = Math.pow(2, -k),
+        i = -1;
+
+    for (const d of data) {
+      var xi = (x(d, ++i, data) + o) * pow2k,
+          yi = (y(d, i, data) + o) * pow2k,
+          wi = +weight(d, i, data);
+      if (wi && xi >= 0 && xi < n && yi >= 0 && yi < m) {
+        var x0 = Math.floor(xi),
+            y0 = Math.floor(yi),
+            xt = xi - x0 - 0.5,
+            yt = yi - y0 - 0.5;
+        values[x0 + y0 * n] += (1 - xt) * (1 - yt) * wi;
+        values[x0 + 1 + y0 * n] += xt * (1 - yt) * wi;
+        values[x0 + 1 + (y0 + 1) * n] += xt * yt * wi;
+        values[x0 + (y0 + 1) * n] += (1 - xt) * yt * wi;
+      }
+    }
+
+    blur2({data: values, width: n, height: m}, r * pow2k);
+    return values;
+  }
+
+  function density(data) {
+    var values = grid(data),
+        tz = threshold(values),
+        pow4k = Math.pow(2, 2 * k);
+
+    // Convert number of thresholds into uniform thresholds.
+    if (!Array.isArray(tz)) {
+      tz = ticks(Number.MIN_VALUE, max(values) / pow4k, tz);
+    }
+
+    return Contours()
+        .size([n, m])
+        .thresholds(tz.map(d => d * pow4k))
+      (values)
+        .map((c, i) => (c.value = +tz[i], transform(c)));
+  }
+
+  density.contours = function(data) {
+    var values = grid(data),
+        contours = Contours().size([n, m]),
+        pow4k = Math.pow(2, 2 * k),
+        contour = value => {
+          value = +value;
+          var c = transform(contours.contour(values, value * pow4k));
+          c.value = value; // preserve exact threshold value
+          return c;
+        };
+    Object.defineProperty(contour, "max", {get: () => max(values) / pow4k});
+    return contour;
+  };
+
+  function transform(geometry) {
+    geometry.coordinates.forEach(transformPolygon);
+    return geometry;
+  }
+
+  function transformPolygon(coordinates) {
+    coordinates.forEach(transformRing);
+  }
+
+  function transformRing(coordinates) {
+    coordinates.forEach(transformPoint);
+  }
+
+  // TODO Optimize.
+  function transformPoint(coordinates) {
+    coordinates[0] = coordinates[0] * Math.pow(2, k) - o;
+    coordinates[1] = coordinates[1] * Math.pow(2, k) - o;
+  }
+
+  function resize() {
+    o = r * 3;
+    n = (dx + o * 2) >> k;
+    m = (dy + o * 2) >> k;
+    return density;
+  }
+
+  density.x = function(_) {
+    return arguments.length ? (x = typeof _ === "function" ? _ : constant(+_), density) : x;
+  };
+
+  density.y = function(_) {
+    return arguments.length ? (y = typeof _ === "function" ? _ : constant(+_), density) : y;
+  };
+
+  density.weight = function(_) {
+    return arguments.length ? (weight = typeof _ === "function" ? _ : constant(+_), density) : weight;
+  };
+
+  density.size = function(_) {
+    if (!arguments.length) return [dx, dy];
+    var _0 = +_[0], _1 = +_[1];
+    if (!(_0 >= 0 && _1 >= 0)) throw new Error("invalid size");
+    return dx = _0, dy = _1, resize();
+  };
+
+  density.cellSize = function(_) {
+    if (!arguments.length) return 1 << k;
+    if (!((_ = +_) >= 1)) throw new Error("invalid cell size");
+    return k = Math.floor(Math.log(_) / Math.LN2), resize();
+  };
+
+  density.thresholds = function(_) {
+    return arguments.length ? (threshold = typeof _ === "function" ? _ : Array.isArray(_) ? constant(slice.call(_)) : constant(_), density) : threshold;
+  };
+
+  density.bandwidth = function(_) {
+    if (!arguments.length) return Math.sqrt(r * (r + 1));
+    if (!((_ = +_) >= 0)) throw new Error("invalid bandwidth");
+    return r = (Math.sqrt(4 * _ * _ + 1) - 1) / 2, resize();
+  };
+
+  return density;
+}