diff --git a/packages/turf-bezier-spline/index.ts b/packages/turf-bezier-spline/index.ts
index c818d9bd53..45b8c78b42 100644
--- a/packages/turf-bezier-spline/index.ts
+++ b/packages/turf-bezier-spline/index.ts
@@ -44,7 +44,7 @@ function bezier<P = Properties>(
   const resolution = options.resolution || 10000;
   const sharpness = options.sharpness || 0.85;
 
-  const coords = [];
+  const coords: [number, number][] = [];
   const points = getGeom(line).coordinates.map((pt) => {
     return { x: pt[0], y: pt[1] };
   });
diff --git a/packages/turf-boolean-equal/package.json b/packages/turf-boolean-equal/package.json
index 74be8413d5..98da3e95c4 100644
--- a/packages/turf-boolean-equal/package.json
+++ b/packages/turf-boolean-equal/package.json
@@ -52,6 +52,7 @@
     "test:tape": "ts-node -r esm test.js"
   },
   "devDependencies": {
+    "@types/geojson-equality": "^0.2.0",
     "@types/tape": "*",
     "benchmark": "*",
     "boolean-shapely": "*",
diff --git a/packages/turf-boolean-overlap/index.ts b/packages/turf-boolean-overlap/index.ts
index 3a7adb8ee5..648727bf27 100644
--- a/packages/turf-boolean-overlap/index.ts
+++ b/packages/turf-boolean-overlap/index.ts
@@ -48,7 +48,7 @@ export default function booleanOverlap(
 
   // features must be not equal
   const equality = new GeojsonEquality({ precision: 6 });
-  if (equality.compare(feature1, feature2)) return false;
+  if (equality.compare(feature1 as any, feature2 as any)) return false;
 
   let overlap = 0;
 
diff --git a/packages/turf-boolean-overlap/package.json b/packages/turf-boolean-overlap/package.json
index 87511d0410..ee53876ad6 100755
--- a/packages/turf-boolean-overlap/package.json
+++ b/packages/turf-boolean-overlap/package.json
@@ -51,6 +51,7 @@
     "test:tape": "ts-node -r esm test.js"
   },
   "devDependencies": {
+    "@types/geojson-equality": "^0.2.0",
     "@types/tape": "*",
     "benchmark": "*",
     "boolean-shapely": "*",
diff --git a/packages/turf-clusters-dbscan/index.ts b/packages/turf-clusters-dbscan/index.ts
index c0b0371eac..8a83078aaa 100644
--- a/packages/turf-clusters-dbscan/index.ts
+++ b/packages/turf-clusters-dbscan/index.ts
@@ -11,10 +11,10 @@ import {
 import clustering from "density-clustering";
 
 export type Dbscan = "core" | "edge" | "noise";
-export interface DbscanProps extends Properties {
+export type DbscanProps = Properties & {
   dbscan?: Dbscan;
   cluster?: number;
-}
+};
 
 /**
  * Takes a set of {@link Point|points} and partition them into clusters according to {@link DBSCAN's|https://en.wikipedia.org/wiki/DBSCAN} data clustering algorithm.
@@ -91,7 +91,7 @@ function clustersDbscan(
     else noisePoint.properties.dbscan = "noise";
   });
 
-  return points;
+  return points as FeatureCollection<Point, DbscanProps>;
 }
 
 export default clustersDbscan;
diff --git a/packages/turf-clusters-dbscan/package.json b/packages/turf-clusters-dbscan/package.json
index aaa634f63f..75b1822bec 100644
--- a/packages/turf-clusters-dbscan/package.json
+++ b/packages/turf-clusters-dbscan/package.json
@@ -56,6 +56,7 @@
   "devDependencies": {
     "@turf/centroid": "^6.4.0",
     "@turf/clusters": "^6.4.0",
+    "@types/density-clustering": "^1.3.0",
     "@types/tape": "*",
     "benchmark": "*",
     "chromatism": "*",
diff --git a/packages/turf-clusters-kmeans/index.ts b/packages/turf-clusters-kmeans/index.ts
index 0384e7abe4..753be25888 100644
--- a/packages/turf-clusters-kmeans/index.ts
+++ b/packages/turf-clusters-kmeans/index.ts
@@ -55,11 +55,7 @@ function clustersKmeans(
   var initialCentroids = data.slice(0, options.numberOfClusters);
 
   // create skmeans clusters
-  var skmeansResult = skmeans(
-    data,
-    options.numberOfClusters,
-    initialCentroids as any // typings are slightly wrong here
-  );
+  var skmeansResult = skmeans(data, options.numberOfClusters, initialCentroids);
 
   // store centroids {clusterId: [number, number]}
   var centroids: Record<string, number[]> = {};
diff --git a/packages/turf-clusters-kmeans/package.json b/packages/turf-clusters-kmeans/package.json
index 38b9b4242f..f70f731154 100644
--- a/packages/turf-clusters-kmeans/package.json
+++ b/packages/turf-clusters-kmeans/package.json
@@ -56,6 +56,7 @@
     "@turf/centroid": "^6.4.0",
     "@turf/clusters": "^6.4.0",
     "@turf/random": "^6.4.0",
+    "@types/skmeans": "^0.11.2",
     "@types/tape": "*",
     "benchmark": "*",
     "chromatism": "*",
diff --git a/packages/turf-polygonize/index.ts b/packages/turf-polygonize/index.ts
index 8cf380bee9..ac95af7ddc 100644
--- a/packages/turf-polygonize/index.ts
+++ b/packages/turf-polygonize/index.ts
@@ -39,8 +39,8 @@ export default function polygonize<T extends LineString | MultiLineString>(
   graph.deleteCutEdges();
 
   // 3. Get all holes and shells
-  const holes = [],
-    shells = [];
+  const holes: EdgeRing[] = [],
+    shells: EdgeRing[] = [];
 
   graph
     .getEdgeRings()
diff --git a/packages/turf-polygonize/lib/Edge.ts b/packages/turf-polygonize/lib/Edge.ts
index 8541e14251..989d86df07 100644
--- a/packages/turf-polygonize/lib/Edge.ts
+++ b/packages/turf-polygonize/lib/Edge.ts
@@ -7,12 +7,12 @@ import EdgeRing from "./EdgeRing";
  * This class is inspired by GEOS's geos::operation::polygonize::PolygonizeDirectedEdge
  */
 export default class Edge {
-  public label: number;
-  public symetric: Edge;
+  public label?: number;
+  public symetric?: Edge;
   public from: Node;
   public to: Node;
-  public next: Edge;
-  public ring: EdgeRing;
+  public next?: Edge;
+  public ring?: EdgeRing;
 
   /**
    * Creates or get the symetric Edge.
@@ -32,7 +32,7 @@ export default class Edge {
    * @param {Node} from - start node of the Edge
    * @param {Node} to - end node of the edge
    */
-  constructor(from, to) {
+  constructor(from: Node, to: Node) {
     this.from = from; //< start
     this.to = to; //< End
 
@@ -61,7 +61,7 @@ export default class Edge {
    * @param {Edge} edge - Another Edge
    * @returns {boolean} - True if Edges are equal, False otherwise
    */
-  isEqual(edge) {
+  isEqual(edge: Edge) {
     return this.from.id === edge.from.id && this.to.id === edge.to.id;
   }
 
@@ -88,7 +88,7 @@ export default class Edge {
    *          0 if the Edges are colinear,
    *          1 otherwise
    */
-  compareTo(edge) {
+  compareTo(edge: Edge) {
     return orientationIndex(
       edge.from.coordinates,
       edge.to.coordinates,
diff --git a/packages/turf-polygonize/lib/EdgeRing.ts b/packages/turf-polygonize/lib/EdgeRing.ts
index eea5425385..1007552dda 100644
--- a/packages/turf-polygonize/lib/EdgeRing.ts
+++ b/packages/turf-polygonize/lib/EdgeRing.ts
@@ -4,7 +4,15 @@ import {
   envelopeContains,
   coordinatesEqual,
 } from "./util";
-import { multiPoint, polygon, point, Polygon, Feature } from "@turf/helpers";
+import {
+  multiPoint,
+  polygon,
+  point,
+  Polygon,
+  Feature,
+  Point,
+  Position,
+} from "@turf/helpers";
 import envelope from "@turf/envelope";
 import booleanPointInPolygon from "@turf/boolean-point-in-polygon";
 import Edge from "./Edge";
@@ -18,13 +26,13 @@ import Edge from "./Edge";
  */
 export default class EdgeRing {
   private edges: Edge[];
-  private polygon: Feature<
+  private polygon?: Feature<
     Polygon,
     {
       [name: string]: any;
     }
   >;
-  private envelope: Feature<
+  private envelope?: Feature<
     Polygon,
     {
       [name: string]: any;
@@ -43,9 +51,7 @@ export default class EdgeRing {
    * @memberof EdgeRing
    * @param {Edge} edge - Edge to be inserted
    */
-  push(edge) {
-    // Emulate Array getter ([]) behaviour
-    this[this.edges.length] = edge;
+  push(edge: Edge) {
     this.edges.push(edge);
     this.polygon = this.envelope = undefined;
   }
@@ -57,7 +63,7 @@ export default class EdgeRing {
    * @param {number} i - Index
    * @returns {Edge} - Edge in the i position
    */
-  get(i) {
+  get(i: number) {
     return this.edges[i];
   }
 
@@ -77,7 +83,7 @@ export default class EdgeRing {
    * @memberof EdgeRing
    * @param {Function} f - The same function to be passed to Array.prototype.forEach
    */
-  forEach(f) {
+  forEach(f: (edge: Edge, index: number, array: Edge[]) => void) {
     this.edges.forEach(f);
   }
 
@@ -88,7 +94,7 @@ export default class EdgeRing {
    * @param {Function} f - The same function to be passed to Array.prototype.map
    * @returns {Array} - The mapped values in the function
    */
-  map(f) {
+  map<T>(f: (edge: Edge, index: number, array: Edge[]) => T): T[] {
     return this.edges.map(f);
   }
 
@@ -99,7 +105,7 @@ export default class EdgeRing {
    * @param {Function} f - The same function to be passed to Array.prototype.some
    * @returns {boolean} - True if an Edge check the condition
    */
-  some(f) {
+  some(f: (edge: Edge, index: number, array: Edge[]) => boolean) {
     return this.edges.some(f);
   }
 
@@ -182,7 +188,10 @@ export default class EdgeRing {
    */
   getEnvelope() {
     if (this.envelope) return this.envelope;
-    return (this.envelope = envelope(this.toPolygon()));
+    return (this.envelope = envelope(this.toPolygon()) as Feature<
+      Polygon,
+      { [name: string]: any }
+    >);
   }
 
   /**
@@ -193,10 +202,13 @@ export default class EdgeRing {
    *
    * @returns {EdgeRing} - EdgeRing which contains the testEdgeRing
    */
-  static findEdgeRingContaining(testEdgeRing, shellList) {
+  static findEdgeRingContaining(
+    testEdgeRing: EdgeRing,
+    shellList: EdgeRing[]
+  ): EdgeRing | undefined {
     const testEnvelope = testEdgeRing.getEnvelope();
 
-    let minEnvelope, minShell;
+    let minEnvelope: Feature<Polygon>, minShell: EdgeRing | undefined;
     shellList.forEach((shell) => {
       const tryEnvelope = shell.getEnvelope();
 
@@ -206,12 +218,18 @@ export default class EdgeRing {
       if (envelopeIsEqual(tryEnvelope, testEnvelope)) return;
 
       if (envelopeContains(tryEnvelope, testEnvelope)) {
-        const testPoint = testEdgeRing
-          .map((edge) => edge.from.coordinates)
-          .find(
-            (pt) =>
-              !shell.some((edge) => coordinatesEqual(pt, edge.from.coordinates))
-          );
+        const testEdgeRingCoordinates = testEdgeRing.map(
+          (edge) => edge.from.coordinates
+        );
+
+        let testPoint: Position | undefined;
+        for (const pt of testEdgeRingCoordinates) {
+          if (
+            !shell.some((edge) => coordinatesEqual(pt, edge.from.coordinates))
+          ) {
+            testPoint = pt;
+          }
+        }
 
         if (testPoint && shell.inside(point(testPoint))) {
           if (!minShell || envelopeContains(minEnvelope, tryEnvelope))
@@ -229,7 +247,7 @@ export default class EdgeRing {
    * @param {Feature<Point>} pt - Point to check if it is inside the edgeRing
    * @returns {boolean} - True if it is inside, False otherwise
    */
-  inside(pt) {
+  inside(pt: Feature<Point>) {
     return booleanPointInPolygon(pt, this.toPolygon());
   }
 }
diff --git a/packages/turf-polygonize/lib/Graph.ts b/packages/turf-polygonize/lib/Graph.ts
index ca0e524fe8..6f2e6e1b09 100644
--- a/packages/turf-polygonize/lib/Graph.ts
+++ b/packages/turf-polygonize/lib/Graph.ts
@@ -8,6 +8,7 @@ import {
   LineString,
   MultiLineString,
   Feature,
+  GeoJSONObject,
 } from "@turf/helpers";
 
 /**
@@ -16,7 +17,7 @@ import {
  * @param {GeoJSON} geoJson - input geoJson.
  * @throws {Error} if geoJson is invalid.
  */
-function validateGeoJson(geoJson) {
+function validateGeoJson(geoJson: GeoJSONObject) {
   if (!geoJson) throw new Error("No geojson passed");
 
   if (
@@ -153,8 +154,8 @@ export default class Graph {
 
     // Cut-edges (bridges) are edges where both edges have the same label
     this.edges.forEach((edge) => {
-      if (edge.label === edge.symetric.label) {
-        this.removeEdge(edge.symetric);
+      if (edge.label === edge.symetric!.label) {
+        this.removeEdge(edge.symetric!);
         this.removeEdge(edge);
       }
     });
@@ -177,7 +178,7 @@ export default class Graph {
       node.getOuterEdges().forEach((edge, i) => {
         node.getOuterEdge(
           (i === 0 ? node.getOuterEdges().length : i) - 1
-        ).symetric.next = edge;
+        ).symetric!.next = edge;
       });
     }
   }
@@ -205,7 +206,7 @@ export default class Graph {
 
       if (de.label === label) outDE = de;
 
-      if (sym.label === label) inDE = sym;
+      if (sym!.label === label) inDE = sym;
 
       if (!outDE || !inDE)
         // This edge is not in edgering
@@ -234,17 +235,17 @@ export default class Graph {
    * @returns {Edge[]} edges that start rings
    */
   _findLabeledEdgeRings() {
-    const edgeRingStarts = [];
+    const edgeRingStarts: Edge[] = [];
     let label = 0;
     this.edges.forEach((edge) => {
-      if (edge.label >= 0) return;
+      if (edge.label! >= 0) return;
 
       edgeRingStarts.push(edge);
 
       let e = edge;
       do {
         e.label = label;
-        e = e.next;
+        e = e.next!;
       } while (!edge.isEqual(e));
 
       label++;
@@ -269,11 +270,11 @@ export default class Graph {
     this._findLabeledEdgeRings().forEach((edge) => {
       // convertMaximalToMinimalEdgeRings
       this._findIntersectionNodes(edge).forEach((node) => {
-        this._computeNextCCWEdges(node, edge.label);
+        this._computeNextCCWEdges(node, edge.label!);
       });
     });
 
-    const edgeRingList = [];
+    const edgeRingList: EdgeRing[] = [];
 
     // find all edgerings
     this.edges.forEach((edge) => {
@@ -302,7 +303,7 @@ export default class Graph {
 
       if (degree > 1) intersectionNodes.push(edge.from);
 
-      edge = edge.next;
+      edge = edge.next!;
     } while (!startEdge.isEqual(edge));
 
     return intersectionNodes;
@@ -321,7 +322,7 @@ export default class Graph {
     do {
       edgeRing.push(edge);
       edge.ring = edgeRing;
-      edge = edge.next;
+      edge = edge.next!;
     } while (!startEdge.isEqual(edge));
 
     return edgeRing;
diff --git a/packages/turf-polygonize/lib/Node.ts b/packages/turf-polygonize/lib/Node.ts
index 96f3a04c21..d377e4858a 100644
--- a/packages/turf-polygonize/lib/Node.ts
+++ b/packages/turf-polygonize/lib/Node.ts
@@ -25,11 +25,11 @@ export default class Node {
     this.outerEdgesSorted = false; //< {Boolean} flag that stores if the outer Edges had been sorted
   }
 
-  removeInnerEdge(edge) {
+  removeInnerEdge(edge: Edge) {
     this.innerEdges = this.innerEdges.filter((e) => e.from.id !== edge.from.id);
   }
 
-  removeOuterEdge(edge) {
+  removeOuterEdge(edge: Edge) {
     this.outerEdges = this.outerEdges.filter((e) => e.to.id !== edge.to.id);
   }
 
@@ -39,7 +39,7 @@ export default class Node {
    * @memberof Node
    * @param {Edge} edge - Edge to add as an outerEdge.
    */
-  addOuterEdge(edge) {
+  addOuterEdge(edge: Edge) {
     this.outerEdges.push(edge);
     this.outerEdgesSorted = false;
   }
@@ -115,12 +115,12 @@ export default class Node {
     return this.outerEdges;
   }
 
-  getOuterEdge(i) {
+  getOuterEdge(i: number) {
     this.sortOuterEdges();
     return this.outerEdges[i];
   }
 
-  addInnerEdge(edge) {
+  addInnerEdge(edge: Edge) {
     this.innerEdges.push(edge);
   }
 }
diff --git a/packages/turf-polygonize/lib/util.ts b/packages/turf-polygonize/lib/util.ts
index 1bb3945941..c8502544af 100644
--- a/packages/turf-polygonize/lib/util.ts
+++ b/packages/turf-polygonize/lib/util.ts
@@ -1,5 +1,5 @@
 import booleanPointInPolygon from "@turf/boolean-point-in-polygon";
-import { point } from "@turf/helpers";
+import { Feature, point, Polygon } from "@turf/helpers";
 
 // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sign#Polyfill
 function mathSign(x: number) {
@@ -22,7 +22,7 @@ function mathSign(x: number) {
  *    -1 if q is cw (right) from p1->p2,
  *     0 if q is colinear with p1->p2
  */
-function orientationIndex(p1, p2, q) {
+export function orientationIndex(p1: number[], p2: number[], q: number[]) {
   const dx1 = p2[0] - p1[0],
     dy1 = p2[1] - p1[1],
     dx2 = q[0] - p2[0],
@@ -40,17 +40,20 @@ function orientationIndex(p1, p2, q) {
  * @param {Feature<Polygon>} env2 - Envelope
  * @returns {boolean} - True if the envelopes are equal
  */
-function envelopeIsEqual(env1, env2) {
-  const envX1 = env1.geometry.coordinates.map((c) => c[0]),
-    envY1 = env1.geometry.coordinates.map((c) => c[1]),
-    envX2 = env2.geometry.coordinates.map((c) => c[0]),
-    envY2 = env2.geometry.coordinates.map((c) => c[1]);
+export function envelopeIsEqual(
+  env1: Feature<Polygon>,
+  env2: Feature<Polygon>
+) {
+  const envX1 = env1.geometry.coordinates[0].map((c) => c[0]),
+    envY1 = env1.geometry.coordinates[0].map((c) => c[1]),
+    envX2 = env2.geometry.coordinates[0].map((c) => c[0]),
+    envY2 = env2.geometry.coordinates[0].map((c) => c[1]);
 
   return (
-    Math.max(null, envX1) === Math.max(null, envX2) &&
-    Math.max(null, envY1) === Math.max(null, envY2) &&
-    Math.min(null, envX1) === Math.min(null, envX2) &&
-    Math.min(null, envY1) === Math.min(null, envY2)
+    Math.max.apply(null, envX1) === Math.max.apply(null, envX2) &&
+    Math.max.apply(null, envY1) === Math.max.apply(null, envY2) &&
+    Math.min.apply(null, envX1) === Math.min.apply(null, envX2) &&
+    Math.min.apply(null, envY1) === Math.min.apply(null, envY2)
   );
 }
 
@@ -65,7 +68,10 @@ function envelopeIsEqual(env1, env2) {
  * @param {Feature<Polygon>} env - Envelope
  * @returns {boolean} - True if env is contained in self
  */
-function envelopeContains(self, env) {
+export function envelopeContains(
+  self: Feature<Polygon>,
+  env: Feature<Polygon>
+) {
   return env.geometry.coordinates[0].every((c) =>
     booleanPointInPolygon(point(c), self)
   );
@@ -78,13 +84,6 @@ function envelopeContains(self, env) {
  * @param {number[]} coord2 - Second coordinate
  * @returns {boolean} - True if coordinates are equal
  */
-function coordinatesEqual(coord1, coord2) {
+export function coordinatesEqual(coord1: number[], coord2: number[]) {
   return coord1[0] === coord2[0] && coord1[1] === coord2[1];
 }
-
-export {
-  orientationIndex,
-  envelopeIsEqual,
-  envelopeContains,
-  coordinatesEqual,
-};
diff --git a/tsconfig.shared.json b/tsconfig.shared.json
index 2ab59d2a94..e351d2abb2 100644
--- a/tsconfig.shared.json
+++ b/tsconfig.shared.json
@@ -4,7 +4,7 @@
     "module": "commonjs",
     "declaration": true,
     "esModuleInterop": true,
-    "strict": false,
+    "strict": true,
     "moduleResolution": "node"
   }
 }
diff --git a/yarn.lock b/yarn.lock
index ffc508f86b..ac0bc13642 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1200,6 +1200,11 @@
   resolved "https://registry.yarnpkg.com/@types/deep-equal/-/deep-equal-1.0.1.tgz#71cfabb247c22bcc16d536111f50c0ed12476b03"
   integrity sha512-mMUu4nWHLBlHtxXY17Fg6+ucS/MnndyOWyOe7MmwkoMYxvfQU2ajtRaEvqSUv+aVkMqH/C0NCI8UoVfRNQ10yg==
 
+"@types/density-clustering@^1.3.0":
+  version "1.3.0"
+  resolved "https://registry.yarnpkg.com/@types/density-clustering/-/density-clustering-1.3.0.tgz#43788f753498cc1912619bbaa942b8f68a06f244"
+  integrity sha512-3dBJlxpR8vHFSA4C0JDruxl2UqdSVoP3shJdqWctaXhS+pli6NeQB2zweoRyO/QIYxgwYaAuqGTb/Henq6mvcA==
+
 "@types/estree@*", "@types/estree@^0.0.48":
   version "0.0.48"
   resolved "https://registry.yarnpkg.com/@types/estree/-/estree-0.0.48.tgz#18dc8091b285df90db2f25aa7d906cfc394b7f74"
@@ -1215,6 +1220,13 @@
   resolved "https://registry.yarnpkg.com/@types/events/-/events-3.0.0.tgz#2862f3f58a9a7f7c3e78d79f130dd4d71c25c2a7"
   integrity sha512-EaObqwIvayI5a8dCzhFrjKzVwKLxjoG9T6Ppd5CEo07LRKfQ8Yokw54r5+Wq7FaBQ+yXRvQAYPrHwya1/UFt9g==
 
+"@types/geojson-equality@^0.2.0":
+  version "0.2.0"
+  resolved "https://registry.yarnpkg.com/@types/geojson-equality/-/geojson-equality-0.2.0.tgz#2c7d411f534bee6bf2e7689c14c4c6f3dced2a8c"
+  integrity sha512-JH6J3S3MW79WKbEuSrwosuu3oUnC6mujFL7UosxlcIWIHwC77Zg1+edkC4oZTRHXAp8SfqTisIEPBBOWLAwlzw==
+  dependencies:
+    "@types/geojson" "*"
+
 "@types/geojson@*":
   version "7946.0.1"
   resolved "https://registry.yarnpkg.com/@types/geojson/-/geojson-7946.0.1.tgz#1fc41280e42f08f0d568401a556bc97c34f5262e"
@@ -1300,6 +1312,11 @@
   dependencies:
     "@types/node" "*"
 
+"@types/skmeans@^0.11.2":
+  version "0.11.2"
+  resolved "https://registry.yarnpkg.com/@types/skmeans/-/skmeans-0.11.2.tgz#33b74ff650a166ea86ae4644d8ce16c50a93e603"
+  integrity sha512-VFOatc1ITAAaYjslFTow+2qJckJROAa5eUvivcTZ4wnSLELFCVt3ezwC0ENl21A0SfqclhKeK4unthZ3uTBCCg==
+
 "@types/tape@*":
   version "4.2.32"
   resolved "https://registry.yarnpkg.com/@types/tape/-/tape-4.2.32.tgz#1188330d22c4e822648c344faa070277737982d9"