diff --git a/src/scripts/options/about.js b/src/modules/ui/about.ts
similarity index 88%
rename from src/scripts/options/about.js
rename to src/modules/ui/about.ts
index 4db49c01..63fa9e9c 100644
--- a/src/scripts/options/about.js
+++ b/src/modules/ui/about.ts
@@ -1,3 +1,6 @@
+import {link} from "utils/linkUtils";
+import {byId} from "utils/shorthands";
+
 // show info about the generator in a popup
 export function showAboutDialog() {
   const Discord = link("https://discordapp.com/invite/X7E84HU", "Discord");
@@ -11,7 +14,9 @@ export function showAboutDialog() {
   const QAA = link("https://github.com/Azgaar/Fantasy-Map-Generator/wiki/Q&A", "Q&A page");
   const VideoTutorial = link("https://youtube.com/playlist?list=PLtgiuDC8iVR2gIG8zMTRn7T_L0arl9h1C", "Video tutorial");
 
-  alertMessage.innerHTML = /* html */ `<b>Fantasy Map Generator</b> (FMG) is a free open-source application. It means that you own all created maps and can use them as
+  byId(
+    "alertMessage"
+  )!.innerHTML = /* html */ `<b>Fantasy Map Generator</b> (FMG) is a free open-source application. It means that you own all created maps and can use them as
     you wish.
 
     <p>
diff --git a/src/scripts/hotkeys.ts b/src/scripts/hotkeys.ts
index ef947035..39970ccf 100644
--- a/src/scripts/hotkeys.ts
+++ b/src/scripts/hotkeys.ts
@@ -1,7 +1,6 @@
 import {openDialog} from "dialogs";
 import {toggleLayer} from "layers";
-// @ts-expect-error js module
-import {showAboutDialog} from "scripts/options/about";
+import {showAboutDialog} from "modules/ui/about";
 import {byId} from "utils/shorthands";
 import {closeDialogs} from "dialogs/utils";
 import {minmax} from "utils/numberUtils";
diff --git a/src/scripts/rankCells.js b/src/scripts/rankCells.ts
similarity index 99%
rename from src/scripts/rankCells.js
rename to src/scripts/rankCells.ts
index 37c3f214..b76c7501 100644
--- a/src/scripts/rankCells.js
+++ b/src/scripts/rankCells.ts
@@ -7,6 +7,7 @@ import {normalize} from "utils/numberUtils";
 export function rankCells() {
   TIME && console.time("rankCells");
   const {cells, features} = pack;
+
   cells.s = new Int16Array(cells.i.length); // cell suitability array
   cells.pop = new Float32Array(cells.i.length); // cell population array
 
diff --git a/src/types/common.d.ts b/src/types/common.d.ts
index f8a7c118..f5a97eac 100644
--- a/src/types/common.d.ts
+++ b/src/types/common.d.ts
@@ -6,7 +6,8 @@ interface Dict<T> {
   [key: string]: T;
 }
 
-type IntArray = Uint8Array | Uint16Array | Uint32Array;
+type UintArray = Uint8Array | Uint16Array | Uint32Array;
+type IntArray = Int8Array | Int16Array | Int32Array;
 
 type RGB = `rgb(${number}, ${number}, ${number})`;
 type Hex = `#${string}`;
diff --git a/src/types/grid.d.ts b/src/types/grid.d.ts
index bb4ba37e..82fd30f5 100644
--- a/src/types/grid.d.ts
+++ b/src/types/grid.d.ts
@@ -8,19 +8,19 @@ interface IGrid {
     c: number[][];
   };
   cells: {
-    i: IntArray;
-    b: IntArray;
+    i: UintArray;
+    b: UintArray;
     c: number[][];
     v: number[][];
-    h: IntArray;
-    t: IntArray;
-    f: IntArray;
-    temp: IntArray;
-    prec: IntArray;
+    h: UintArray;
+    t: UintArray;
+    f: UintArray;
+    temp: UintArray;
+    prec: UintArray;
   };
-  features: IFeature[];
+  features: IGridFeature[];
 }
-interface IFeature {
+interface IGridFeature {
   i: number;
   land: boolean;
   border: boolean;
diff --git a/src/types/pack.d.ts b/src/types/pack.d.ts
index d58c54f5..34c48b84 100644
--- a/src/types/pack.d.ts
+++ b/src/types/pack.d.ts
@@ -4,24 +4,26 @@ interface IPack {
     v: number[][];
     c: number[][];
   };
-  features: IFeature[];
+  features: TPackFeature[];
   cells: {
-    i: IntArray;
+    i: UintArray;
     p: TPoints;
     v: number[][];
     c: number[][];
-    g: IntArray;
-    h: IntArray;
-    t: IntArray;
-    f: IntArray;
-    biome: IntArray;
+    g: UintArray;
+    h: UintArray;
+    t: UintArray;
+    f: UintArray;
+    s: IntArray;
     pop: Float32Array;
-    area: IntArray;
-    state: IntArray;
-    culture: IntArray;
-    religion: IntArray;
-    province: IntArray;
-    burg: IntArray;
+    fl: UintArray;
+    biome: UintArray;
+    area: UintArray;
+    state: UintArray;
+    culture: UintArray;
+    religion: UintArray;
+    province: UintArray;
+    burg: UintArray;
     q: d3.Quadtree<number[]>;
   };
   states: IState[];
@@ -32,11 +34,35 @@ interface IPack {
   religions: IReligion[];
 }
 
-interface IFeature {
-  i: number;
+interface IPackFeatureBase {
+  i: number; // feature id starting from 1
+  border: boolean; // if touches map border
+  cells: number; // number of cells
+  firstCell: number; // index of the top left cell
+  vertices: number[]; // indexes of perimetric vertices
+}
+
+interface IPackFeatureOcean extends IPackFeatureBase {
+  land: false;
+  type: "ocean";
+  group: "ocean";
+}
+
+interface IPackFeatureIsland extends IPackFeatureBase {
+  land: true;
+  type: "island";
+  group: "continent" | "island" | "isle" | "lake_island";
+}
+
+interface IPackFeatureLake extends IPackFeatureBase {
+  land: false;
+  type: "lake";
+  group: "freshwater" | "salt" | "frozen" | "dry" | "sinkhole" | "lava";
   name: string;
 }
 
+type TPackFeature = IPackFeatureOcean | IPackFeatureIsland | IPackFeatureLake;
+
 interface IState {
   i: number;
   name: string;