Index: node_modules/d3-contour/src/area.js
===================================================================
--- node_modules/d3-contour/src/area.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/area.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,5 @@
+export default function(ring) {
+  var i = 0, n = ring.length, area = ring[n - 1][1] * ring[0][0] - ring[n - 1][0] * ring[0][1];
+  while (++i < n) area += ring[i - 1][1] * ring[i][0] - ring[i - 1][0] * ring[i][1];
+  return area;
+}
Index: node_modules/d3-contour/src/array.js
===================================================================
--- node_modules/d3-contour/src/array.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/array.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,3 @@
+var array = Array.prototype;
+
+export var slice = array.slice;
Index: node_modules/d3-contour/src/ascending.js
===================================================================
--- node_modules/d3-contour/src/ascending.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/ascending.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,3 @@
+export default function(a, b) {
+  return a - b;
+}
Index: node_modules/d3-contour/src/constant.js
===================================================================
--- node_modules/d3-contour/src/constant.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/constant.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,1 @@
+export default x => () => x;
Index: node_modules/d3-contour/src/contains.js
===================================================================
--- node_modules/d3-contour/src/contains.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/contains.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,27 @@
+export default function(ring, hole) {
+  var i = -1, n = hole.length, c;
+  while (++i < n) if (c = ringContains(ring, hole[i])) return c;
+  return 0;
+}
+
+function ringContains(ring, point) {
+  var x = point[0], y = point[1], contains = -1;
+  for (var i = 0, n = ring.length, j = n - 1; i < n; j = i++) {
+    var pi = ring[i], xi = pi[0], yi = pi[1], pj = ring[j], xj = pj[0], yj = pj[1];
+    if (segmentContains(pi, pj, point)) return 0;
+    if (((yi > y) !== (yj > y)) && ((x < (xj - xi) * (y - yi) / (yj - yi) + xi))) contains = -contains;
+  }
+  return contains;
+}
+
+function segmentContains(a, b, c) {
+  var i; return collinear(a, b, c) && within(a[i = +(a[0] === b[0])], c[i], b[i]);
+}
+
+function collinear(a, b, c) {
+  return (b[0] - a[0]) * (c[1] - a[1]) === (c[0] - a[0]) * (b[1] - a[1]);
+}
+
+function within(p, q, r) {
+  return p <= q && q <= r || r <= q && q <= p;
+}
Index: node_modules/d3-contour/src/contours.js
===================================================================
--- node_modules/d3-contour/src/contours.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/contours.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,225 @@
+import {extent, nice, thresholdSturges, ticks} from "d3-array";
+import {slice} from "./array.js";
+import ascending from "./ascending.js";
+import area from "./area.js";
+import constant from "./constant.js";
+import contains from "./contains.js";
+import noop from "./noop.js";
+
+var cases = [
+  [],
+  [[[1.0, 1.5], [0.5, 1.0]]],
+  [[[1.5, 1.0], [1.0, 1.5]]],
+  [[[1.5, 1.0], [0.5, 1.0]]],
+  [[[1.0, 0.5], [1.5, 1.0]]],
+  [[[1.0, 1.5], [0.5, 1.0]], [[1.0, 0.5], [1.5, 1.0]]],
+  [[[1.0, 0.5], [1.0, 1.5]]],
+  [[[1.0, 0.5], [0.5, 1.0]]],
+  [[[0.5, 1.0], [1.0, 0.5]]],
+  [[[1.0, 1.5], [1.0, 0.5]]],
+  [[[0.5, 1.0], [1.0, 0.5]], [[1.5, 1.0], [1.0, 1.5]]],
+  [[[1.5, 1.0], [1.0, 0.5]]],
+  [[[0.5, 1.0], [1.5, 1.0]]],
+  [[[1.0, 1.5], [1.5, 1.0]]],
+  [[[0.5, 1.0], [1.0, 1.5]]],
+  []
+];
+
+export default function() {
+  var dx = 1,
+      dy = 1,
+      threshold = thresholdSturges,
+      smooth = smoothLinear;
+
+  function contours(values) {
+    var tz = threshold(values);
+
+    // Convert number of thresholds into uniform thresholds.
+    if (!Array.isArray(tz)) {
+      const e = extent(values, finite);
+      tz = ticks(...nice(e[0], e[1], tz), tz);
+      while (tz[tz.length - 1] >= e[1]) tz.pop();
+      while (tz[1] < e[0]) tz.shift();
+    } else {
+      tz = tz.slice().sort(ascending);
+    }
+
+    return tz.map(value => contour(values, value));
+  }
+
+  // Accumulate, smooth contour rings, assign holes to exterior rings.
+  // Based on https://github.com/mbostock/shapefile/blob/v0.6.2/shp/polygon.js
+  function contour(values, value) {
+    const v = value == null ? NaN : +value;
+    if (isNaN(v)) throw new Error(`invalid value: ${value}`);
+
+    var polygons = [],
+        holes = [];
+
+    isorings(values, v, function(ring) {
+      smooth(ring, values, v);
+      if (area(ring) > 0) polygons.push([ring]);
+      else holes.push(ring);
+    });
+
+    holes.forEach(function(hole) {
+      for (var i = 0, n = polygons.length, polygon; i < n; ++i) {
+        if (contains((polygon = polygons[i])[0], hole) !== -1) {
+          polygon.push(hole);
+          return;
+        }
+      }
+    });
+
+    return {
+      type: "MultiPolygon",
+      value: value,
+      coordinates: polygons
+    };
+  }
+
+  // Marching squares with isolines stitched into rings.
+  // Based on https://github.com/topojson/topojson-client/blob/v3.0.0/src/stitch.js
+  function isorings(values, value, callback) {
+    var fragmentByStart = new Array,
+        fragmentByEnd = new Array,
+        x, y, t0, t1, t2, t3;
+
+    // Special case for the first row (y = -1, t2 = t3 = 0).
+    x = y = -1;
+    t1 = above(values[0], value);
+    cases[t1 << 1].forEach(stitch);
+    while (++x < dx - 1) {
+      t0 = t1, t1 = above(values[x + 1], value);
+      cases[t0 | t1 << 1].forEach(stitch);
+    }
+    cases[t1 << 0].forEach(stitch);
+
+    // General case for the intermediate rows.
+    while (++y < dy - 1) {
+      x = -1;
+      t1 = above(values[y * dx + dx], value);
+      t2 = above(values[y * dx], value);
+      cases[t1 << 1 | t2 << 2].forEach(stitch);
+      while (++x < dx - 1) {
+        t0 = t1, t1 = above(values[y * dx + dx + x + 1], value);
+        t3 = t2, t2 = above(values[y * dx + x + 1], value);
+        cases[t0 | t1 << 1 | t2 << 2 | t3 << 3].forEach(stitch);
+      }
+      cases[t1 | t2 << 3].forEach(stitch);
+    }
+
+    // Special case for the last row (y = dy - 1, t0 = t1 = 0).
+    x = -1;
+    t2 = values[y * dx] >= value;
+    cases[t2 << 2].forEach(stitch);
+    while (++x < dx - 1) {
+      t3 = t2, t2 = above(values[y * dx + x + 1], value);
+      cases[t2 << 2 | t3 << 3].forEach(stitch);
+    }
+    cases[t2 << 3].forEach(stitch);
+
+    function stitch(line) {
+      var start = [line[0][0] + x, line[0][1] + y],
+          end = [line[1][0] + x, line[1][1] + y],
+          startIndex = index(start),
+          endIndex = index(end),
+          f, g;
+      if (f = fragmentByEnd[startIndex]) {
+        if (g = fragmentByStart[endIndex]) {
+          delete fragmentByEnd[f.end];
+          delete fragmentByStart[g.start];
+          if (f === g) {
+            f.ring.push(end);
+            callback(f.ring);
+          } else {
+            fragmentByStart[f.start] = fragmentByEnd[g.end] = {start: f.start, end: g.end, ring: f.ring.concat(g.ring)};
+          }
+        } else {
+          delete fragmentByEnd[f.end];
+          f.ring.push(end);
+          fragmentByEnd[f.end = endIndex] = f;
+        }
+      } else if (f = fragmentByStart[endIndex]) {
+        if (g = fragmentByEnd[startIndex]) {
+          delete fragmentByStart[f.start];
+          delete fragmentByEnd[g.end];
+          if (f === g) {
+            f.ring.push(end);
+            callback(f.ring);
+          } else {
+            fragmentByStart[g.start] = fragmentByEnd[f.end] = {start: g.start, end: f.end, ring: g.ring.concat(f.ring)};
+          }
+        } else {
+          delete fragmentByStart[f.start];
+          f.ring.unshift(start);
+          fragmentByStart[f.start = startIndex] = f;
+        }
+      } else {
+        fragmentByStart[startIndex] = fragmentByEnd[endIndex] = {start: startIndex, end: endIndex, ring: [start, end]};
+      }
+    }
+  }
+
+  function index(point) {
+    return point[0] * 2 + point[1] * (dx + 1) * 4;
+  }
+
+  function smoothLinear(ring, values, value) {
+    ring.forEach(function(point) {
+      var x = point[0],
+          y = point[1],
+          xt = x | 0,
+          yt = y | 0,
+          v1 = valid(values[yt * dx + xt]);
+      if (x > 0 && x < dx && xt === x) {
+        point[0] = smooth1(x, valid(values[yt * dx + xt - 1]), v1, value);
+      }
+      if (y > 0 && y < dy && yt === y) {
+        point[1] = smooth1(y, valid(values[(yt - 1) * dx + xt]), v1, value);
+      }
+    });
+  }
+
+  contours.contour = contour;
+
+  contours.size = function(_) {
+    if (!arguments.length) return [dx, dy];
+    var _0 = Math.floor(_[0]), _1 = Math.floor(_[1]);
+    if (!(_0 >= 0 && _1 >= 0)) throw new Error("invalid size");
+    return dx = _0, dy = _1, contours;
+  };
+
+  contours.thresholds = function(_) {
+    return arguments.length ? (threshold = typeof _ === "function" ? _ : Array.isArray(_) ? constant(slice.call(_)) : constant(_), contours) : threshold;
+  };
+
+  contours.smooth = function(_) {
+    return arguments.length ? (smooth = _ ? smoothLinear : noop, contours) : smooth === smoothLinear;
+  };
+
+  return contours;
+}
+
+// When computing the extent, ignore infinite values (as well as invalid ones).
+function finite(x) {
+  return isFinite(x) ? x : NaN;
+}
+
+// Is the (possibly invalid) x greater than or equal to the (known valid) value?
+// Treat any invalid value as below negative infinity.
+function above(x, value) {
+  return x == null ? false : +x >= value;
+}
+
+// During smoothing, treat any invalid value as negative infinity.
+function valid(v) {
+  return v == null || isNaN(v = +v) ? -Infinity : v;
+}
+
+function smooth1(x, v0, v1, value) {
+  const a = value - v0;
+  const b = v1 - v0;
+  const d = isFinite(a) || isFinite(b) ? a / b : Math.sign(a) / Math.sign(b);
+  return isNaN(d) ? x : x + d - 0.5;
+}
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;
+}
Index: node_modules/d3-contour/src/index.js
===================================================================
--- node_modules/d3-contour/src/index.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/index.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,2 @@
+export {default as contours} from "./contours.js";
+export {default as contourDensity} from "./density.js";
Index: node_modules/d3-contour/src/noop.js
===================================================================
--- node_modules/d3-contour/src/noop.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-contour/src/noop.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,1 @@
+export default function() {}