diff --git a/back/src/Controller/IoSocketController.ts b/back/src/Controller/IoSocketController.ts
index e18a5beb..878c6c75 100644
--- a/back/src/Controller/IoSocketController.ts
+++ b/back/src/Controller/IoSocketController.ts
@@ -20,6 +20,7 @@ import {isWebRtcSignalMessageInterface} from "../Model/Websocket/WebRtcSignalMes
 import {UserInGroupInterface} from "../Model/Websocket/UserInGroupInterface";
 import {uuid} from 'uuidv4';
 import {isUserMovesInterface} from "../Model/Websocket/UserMovesMessage";
+import {isViewport} from "../Model/Websocket/ViewportMessage";
 
 enum SockerIoEvent {
     CONNECTION = "connection",
@@ -212,22 +213,16 @@ export class IoSocketController {
                     //join new previous room
                     const world = this.joinRoom(Client, roomId, message.position);
 
-                    //add function to refresh position user in real time.
-                    //this.refreshUserPosition(Client);
-
-                    const messageUserJoined = new MessageUserJoined(Client.userId, Client.name, Client.characterLayers, Client.position);
-
-                    socket.to(roomId).emit(SockerIoEvent.JOIN_ROOM, messageUserJoined);
-
-                    // The answer shall contain the list of all users of the room with their positions:
-                    const listOfUsers = Array.from(world.getUsers(), ([key, user]) => {
+                    const users = world.setViewport(Client, message.viewport);
+                    const listOfUsers = users.map((user: UserInterface) => {
                         const player: ExSocketInterface|undefined = this.sockets.get(user.id);
                         if (player === undefined) {
                             console.warn('Something went wrong. The World contains a user "'+user.id+"' but this user does not exist in the sockets list!");
                             return null;
                         }
                         return new MessageUserPosition(user.id, player.name, player.characterLayers, player.position);
-                    }).filter((item: MessageUserPosition|null) => item !== null);
+                    }, users);
+
                     answerFn(listOfUsers);
                 } catch (e) {
                     console.error('An error occurred on "join_room" event');
@@ -235,6 +230,30 @@ export class IoSocketController {
                 }
             });
 
+            socket.on(SockerIoEvent.SET_VIEWPORT, (message: unknown): void => {
+                try {
+                    //console.log('SET_VIEWPORT')
+                    if (!isViewport(message)) {
+                        socket.emit(SockerIoEvent.MESSAGE_ERROR, {message: 'Invalid SET_VIEWPORT message.'});
+                        console.warn('Invalid SET_VIEWPORT message received: ', message);
+                        return;
+                    }
+
+                    const Client = (socket as ExSocketInterface);
+                    Client.viewport = message;
+
+                    const world = this.Worlds.get(Client.roomId);
+                    if (!world) {
+                        console.error("Could not find world with id '", Client.roomId, "'");
+                        return;
+                    }
+                    world.setViewport(Client, Client.viewport);
+                } catch (e) {
+                    console.error('An error occurred on "SET_VIEWPORT" event');
+                    console.error(e);
+                }
+            });
+
             socket.on(SockerIoEvent.USER_POSITION, (userMovesMessage: unknown): void => {
                 console.log(SockerIoEvent.USER_POSITION, userMovesMessage);
                 try {
@@ -257,19 +276,7 @@ export class IoSocketController {
                         return;
                     }
                     world.updatePosition(Client, Client.position);
-
-                    const clientsInRoom = this.Io.sockets.adapter.rooms[Client.roomId];
-                    console.log('clientsInRoom', clientsInRoom);
-                    for (const clientId in clientsInRoom.sockets) {
-                        console.log('client: %s', clientId);
-                        const targetSocket = this.Io.sockets.connected[clientId] as ExSocketInterface;
-                        if (socket === targetSocket) {
-                            continue;
-                        }
-                        //targetSocket.emit(SockerIoEvent.USER_MOVED, new MessageUserMoved(Client.userId, Client.position));
-                        targetSocket.emitInBatch(SockerIoEvent.USER_MOVED, new MessageUserMoved(Client.userId, Client.position));
-                    }
-                    //socket.to(Client.roomId).emit(SockerIoEvent.USER_MOVED, new MessageUserMoved(Client.userId, Client.position));
+                    world.setViewport(Client, Client.viewport);
                 } catch (e) {
                     console.error('An error occurred on "user_position" event');
                     console.error(e);
@@ -404,8 +411,6 @@ export class IoSocketController {
         // leave previous room and world
         if(Client.roomId){
             try {
-                Client.to(Client.roomId).emit(SockerIoEvent.USER_LEFT, Client.userId);
-
                 //user leave previous world
                 const world: World | undefined = this.Worlds.get(Client.roomId);
                 if (world) {
@@ -441,6 +446,25 @@ export class IoSocketController {
                 this.sendUpdateGroupEvent(group);
             }, (groupUuid: string, lastUser: UserInterface) => {
                 this.sendDeleteGroupEvent(groupUuid, lastUser);
+            }, (user, listener) => {
+                const clientUser = this.searchClientByIdOrFail(user.id);
+                const clientListener = this.searchClientByIdOrFail(listener.id);
+                const messageUserJoined = new MessageUserJoined(clientUser.userId, clientUser.name, clientUser.characterLayers, clientUser.position);
+
+                clientListener.emit(SockerIoEvent.JOIN_ROOM, messageUserJoined);
+                //console.log("Sending JOIN_ROOM event");
+            }, (user, position, listener) => {
+                const clientUser = this.searchClientByIdOrFail(user.id);
+                const clientListener = this.searchClientByIdOrFail(listener.id);
+
+                clientListener.emitInBatch(SockerIoEvent.USER_MOVED, new MessageUserMoved(clientUser.userId, clientUser.position));
+                //console.log("Sending USER_MOVED event");
+            }, (user, listener) => {
+                const clientUser = this.searchClientByIdOrFail(user.id);
+                const clientListener = this.searchClientByIdOrFail(listener.id);
+
+                clientListener.emit(SockerIoEvent.USER_LEFT, clientUser.userId);
+                //console.log("Sending USER_LEFT event");
             });
             this.Worlds.set(roomId, world);
         }
diff --git a/back/src/Model/PositionNotifier.ts b/back/src/Model/PositionNotifier.ts
index f5edf8d3..9d6975e3 100644
--- a/back/src/Model/PositionNotifier.ts
+++ b/back/src/Model/PositionNotifier.ts
@@ -34,10 +34,14 @@ export class PositionNotifier {
         }
     }
 
-    public setViewport(user: UserInterface, viewport: ViewportInterface): void {
+    /**
+     * Sets the viewport coordinates.
+     * Returns the list of new users to add
+     */
+    public setViewport(user: UserInterface, viewport: ViewportInterface): UserInterface[] {
         if (viewport.left > viewport.right || viewport.top > viewport.bottom) {
             console.warn('Invalid viewport received: ', viewport);
-            return;
+            return [];
         }
 
         const oldZones = user.listenedZones;
@@ -55,12 +59,17 @@ export class PositionNotifier {
         const addedZones = [...newZones].filter(x => !oldZones.has(x));
         const removedZones = [...oldZones].filter(x => !newZones.has(x));
 
+
+        let users: UserInterface[] = [];
         for (const zone of addedZones) {
             zone.startListening(user);
+            users = users.concat(Array.from(zone.getPlayers()))
         }
         for (const zone of removedZones) {
             zone.stopListening(user);
         }
+
+        return users;
     }
 
     public updatePosition(user: UserInterface, userPosition: PointInterface): void {
@@ -87,6 +96,11 @@ export class PositionNotifier {
         const oldZoneDesc = this.getZoneDescriptorFromCoordinates(user.position.x, user.position.y);
         const oldZone = this.getZone(oldZoneDesc.i, oldZoneDesc.j);
         oldZone.leave(user, null);
+
+        // Also, let's stop listening on viewports
+        for (const zone of user.listenedZones) {
+            zone.stopListening(user);
+        }
     }
 
     private getZone(i: number, j: number): Zone {
diff --git a/back/src/Model/Websocket/JoinRoomMessage.ts b/back/src/Model/Websocket/JoinRoomMessage.ts
index 16613488..2036a441 100644
--- a/back/src/Model/Websocket/JoinRoomMessage.ts
+++ b/back/src/Model/Websocket/JoinRoomMessage.ts
@@ -1,9 +1,11 @@
 import * as tg from "generic-type-guard";
 import {isPointInterface} from "./PointInterface";
+import {isViewport} from "./ViewportMessage";
 
 export const isJoinRoomMessageInterface =
     new tg.IsInterface().withProperties({
         roomId: tg.isString,
         position: isPointInterface,
+        viewport: isViewport
     }).get();
 export type JoinRoomMessageInterface = tg.GuardedType<typeof isJoinRoomMessageInterface>;
diff --git a/back/src/Model/World.ts b/back/src/Model/World.ts
index 0f2cb050..4422e95f 100644
--- a/back/src/Model/World.ts
+++ b/back/src/Model/World.ts
@@ -6,7 +6,9 @@ import {UserInterface} from "./UserInterface";
 import {ExSocketInterface} from "_Model/Websocket/ExSocketInterface";
 import {PositionInterface} from "_Model/PositionInterface";
 import {Identificable} from "_Model/Websocket/Identificable";
-import {Zone} from "_Model/Zone";
+import {UserEntersCallback, UserLeavesCallback, UserMovesCallback, Zone} from "_Model/Zone";
+import {PositionNotifier} from "./PositionNotifier";
+import {ViewportInterface} from "_Model/Websocket/ViewportMessage";
 
 export type ConnectCallback = (user: string, group: Group) => void;
 export type DisconnectCallback = (user: string, group: Group) => void;
@@ -28,12 +30,17 @@ export class World {
     private readonly groupUpdatedCallback: GroupUpdatedCallback;
     private readonly groupDeletedCallback: GroupDeletedCallback;
 
+    private readonly positionNotifier: PositionNotifier;
+
     constructor(connectCallback: ConnectCallback,
                 disconnectCallback: DisconnectCallback,
                 minDistance: number,
                 groupRadius: number,
                 groupUpdatedCallback: GroupUpdatedCallback,
-                groupDeletedCallback: GroupDeletedCallback)
+                groupDeletedCallback: GroupDeletedCallback,
+                onUserEnters: UserEntersCallback,
+                onUserMoves: UserMovesCallback,
+                onUserLeaves: UserLeavesCallback)
     {
         this.users = new Map<string, UserInterface>();
         this.groups = new Set<Group>();
@@ -43,6 +50,8 @@ export class World {
         this.groupRadius = groupRadius;
         this.groupUpdatedCallback = groupUpdatedCallback;
         this.groupDeletedCallback = groupDeletedCallback;
+        // A zone is 10 sprites wide.
+        this.positionNotifier = new PositionNotifier(320, 320, onUserEnters, onUserMoves, onUserLeaves);
     }
 
     public getGroups(): Group[] {
@@ -73,6 +82,10 @@ export class World {
             this.leaveGroup(userObj);
         }
         this.users.delete(user.userId);
+
+        if (userObj !== undefined) {
+            this.positionNotifier.leave(userObj);
+        }
     }
 
     public isEmpty(): boolean {
@@ -85,6 +98,8 @@ export class World {
             return;
         }
 
+        this.positionNotifier.updatePosition(user, userPosition);
+
         user.position = userPosition;
 
         if (user.silent) {
@@ -318,4 +333,12 @@ export class World {
         }
         return 0;
     }*/
+    setViewport(socket : Identificable, viewport: ViewportInterface): UserInterface[] {
+        const user = this.users.get(socket.userId);
+        if(typeof user === 'undefined') {
+            console.warn('In setViewport, could not find user with ID "'+socket.userId+'" in world.');
+            return [];
+        }
+        return this.positionNotifier.setViewport(user, viewport);
+    }
 }
diff --git a/back/src/Model/Zone.ts b/back/src/Model/Zone.ts
index 45d6cdd2..bd748b0f 100644
--- a/back/src/Model/Zone.ts
+++ b/back/src/Model/Zone.ts
@@ -2,9 +2,9 @@ import {UserInterface} from "./UserInterface";
 import {PointInterface} from "_Model/Websocket/PointInterface";
 import {PositionInterface} from "_Model/PositionInterface";
 
-export type UserEntersCallback = (user: UserInterface) => void;
-export type UserMovesCallback = (user: UserInterface, position: PointInterface) => void;
-export type UserLeavesCallback = (user: UserInterface) => void;
+export type UserEntersCallback = (user: UserInterface, listener: UserInterface) => void;
+export type UserMovesCallback = (user: UserInterface, position: PointInterface, listener: UserInterface) => void;
+export type UserLeavesCallback = (user: UserInterface, listener: UserInterface) => void;
 
 export class Zone {
     private players: Set<UserInterface> = new Set<UserInterface>();
@@ -27,7 +27,7 @@ export class Zone {
     private notifyUserLeft(user: UserInterface, newZone: Zone|null) {
         for (const listener of this.listeners) {
             if (listener !== user && (newZone === null || !listener.listenedZones.has(newZone))) {
-                this.onUserLeaves(user);
+                this.onUserLeaves(user, listener);
             }
         }
     }
@@ -46,40 +46,51 @@ export class Zone {
                 continue;
             }
             if (oldZone === null || !listener.listenedZones.has(oldZone)) {
-                this.onUserEnters(user);
+                this.onUserEnters(user, listener);
             } else {
-                this.onUserMoves(user, position);
+                this.onUserMoves(user, position, listener);
             }
         }
     }
 
     public move(user: UserInterface, position: PointInterface) {
+        if (!this.players.has(user)) {
+            this.players.add(user);
+            const foo = this.players;
+            this.notifyUserEnter(user, null, position);
+            return;
+        }
+
         for (const listener of this.listeners) {
             if (listener !== user) {
-                this.onUserMoves(user,position);
+                this.onUserMoves(user,position, listener);
             }
         }
     }
 
-    public startListening(user: UserInterface): void {
+    public startListening(listener: UserInterface): void {
         for (const player of this.players) {
-            if (player !== user) {
-                this.onUserEnters(user);
+            if (player !== listener) {
+                this.onUserEnters(player, listener);
             }
         }
 
-        this.listeners.add(user);
-        user.listenedZones.add(this);
+        this.listeners.add(listener);
+        listener.listenedZones.add(this);
     }
 
-    public stopListening(user: UserInterface): void {
+    public stopListening(listener: UserInterface): void {
         for (const player of this.players) {
-            if (player !== user) {
-                this.onUserLeaves(user);
+            if (player !== listener) {
+                this.onUserLeaves(player, listener);
             }
         }
 
-        this.listeners.delete(user);
-        user.listenedZones.delete(this);
+        this.listeners.delete(listener);
+        listener.listenedZones.delete(this);
+    }
+
+    public getPlayers(): Set<UserInterface> {
+        return this.players;
     }
 }
diff --git a/back/tests/PositionNotifierTest.ts b/back/tests/PositionNotifierTest.ts
index ac82878b..0b8b466f 100644
--- a/back/tests/PositionNotifierTest.ts
+++ b/back/tests/PositionNotifierTest.ts
@@ -139,13 +139,15 @@ describe("PositionNotifier", () => {
             listenedZones: new Set<Zone>(),
         } as UserInterface;
 
-        positionNotifier.setViewport(user1, {
+        let newUsers = positionNotifier.setViewport(user1, {
             left: 200,
             right: 600,
             top: 100,
             bottom: 500
         });
 
+        expect(newUsers.length).toBe(0);
+
         move(user2, 500, 500, positionNotifier);
 
         expect(enterTriggered).toBe(true);
@@ -178,7 +180,7 @@ describe("PositionNotifier", () => {
         leaveTriggered = false;
 
         // Move the viewport back on the user.
-        positionNotifier.setViewport(user1, {
+        newUsers = positionNotifier.setViewport(user1, {
             left: 200,
             right: 600,
             top: 100,
@@ -189,5 +191,6 @@ describe("PositionNotifier", () => {
         expect(moveTriggered).toBe(false);
         expect(leaveTriggered).toBe(false);
         enterTriggered = false;
+        expect(newUsers.length).toBe(1);
     });
 })
diff --git a/back/tests/WorldTest.ts b/back/tests/WorldTest.ts
index c436eed7..580677c7 100644
--- a/back/tests/WorldTest.ts
+++ b/back/tests/WorldTest.ts
@@ -13,7 +13,7 @@ describe("World", () => {
 
         }
 
-        const world = new World(connect, disconnect, 160, 160, () => {}, () => {});
+        const world = new World(connect, disconnect, 160, 160, () => {}, () => {}, () => {}, () => {}, () => {});
 
         world.join({ userId: "foo" }, new Point(100, 100));
 
@@ -40,7 +40,7 @@ describe("World", () => {
 
         }
 
-        const world = new World(connect, disconnect, 160, 160, () => {}, () => {});
+        const world = new World(connect, disconnect, 160, 160, () => {}, () => {}, () => {}, () => {}, () => {});
 
         world.join({ userId: "foo" }, new Point(100, 100));
 
@@ -69,7 +69,7 @@ describe("World", () => {
             disconnectCallNumber++;
         }
 
-        const world = new World(connect, disconnect, 160, 160, () => {}, () => {});
+        const world = new World(connect, disconnect, 160, 160, () => {}, () => {}, () => {}, () => {}, () => {});
 
         world.join({ userId: "foo" }, new Point(100, 100));
 
diff --git a/back/tsconfig.json b/back/tsconfig.json
index 397bb8a2..de6314a3 100644
--- a/back/tsconfig.json
+++ b/back/tsconfig.json
@@ -12,7 +12,7 @@
     // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
     // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
     // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
-    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
+    "sourceMap": true,                     /* Generates corresponding '.map' file. */
     // "outFile": "./",                       /* Concatenate and emit output to single file. */
     "outDir": "./dist",                        /* Redirect output structure to the directory. */
     // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
diff --git a/front/src/Connection.ts b/front/src/Connection.ts
index c04e5b4f..dee27ae5 100644
--- a/front/src/Connection.ts
+++ b/front/src/Connection.ts
@@ -182,11 +182,15 @@ export class Connection implements Connection {
     }
 
 
-    public joinARoom(roomId: string, startX: number, startY: number, direction: string, moving: boolean): Promise<MessageUserPositionInterface[]> {
+    public joinARoom(roomId: string, startX: number, startY: number, direction: string, moving: boolean, viewport: ViewportInterface): Promise<MessageUserPositionInterface[]> {
         const promise = new Promise<MessageUserPositionInterface[]>((resolve, reject) => {
-            this.socket.emit(EventMessage.JOIN_ROOM, { roomId, position: {x: startX, y: startY, direction, moving }}, (userPositions: MessageUserPositionInterface[]) => {
-                resolve(userPositions);
-            });
+            this.socket.emit(EventMessage.JOIN_ROOM, {
+                    roomId,
+                    position: {x: startX, y: startY, direction, moving },
+                    viewport,
+                }, (userPositions: MessageUserPositionInterface[]) => {
+                    resolve(userPositions);
+                });
         })
         return promise;
     }
@@ -203,6 +207,10 @@ export class Connection implements Connection {
         this.socket.emit(EventMessage.SET_SILENT, silent);
     }
 
+    public setViewport(viewport: ViewportInterface): void {
+        this.socket.emit(EventMessage.SET_VIEWPORT, viewport);
+    }
+
     public onUserJoins(callback: (message: MessageUserJoined) => void): void {
         this.socket.on(EventMessage.JOIN_ROOM, callback);
     }
diff --git a/front/src/Phaser/Game/GameScene.ts b/front/src/Phaser/Game/GameScene.ts
index 595fc9d3..6a6656c2 100644
--- a/front/src/Phaser/Game/GameScene.ts
+++ b/front/src/Phaser/Game/GameScene.ts
@@ -111,7 +111,7 @@ export class GameScene extends Phaser.Scene implements CenterListener {
     private startLayerName: string|undefined;
     private presentationModeSprite!: Sprite;
     private chatModeSprite!: Sprite;
-    private repositionCallback!: (this: Window, ev: UIEvent) => void;
+    private onResizeCallback!: (this: Window, ev: UIEvent) => void;
     private gameMap!: GameMap;
 
     static createFromUrl(mapUrlFile: string, instance: string, key: string|null = null): GameScene {
@@ -226,7 +226,7 @@ export class GameScene extends Phaser.Scene implements CenterListener {
 
                 this.scene.stop(this.scene.key);
                 this.scene.remove(this.scene.key);
-                window.removeEventListener('resize', this.repositionCallback);
+                window.removeEventListener('resize', this.onResizeCallback);
             })
 
             // When connection is performed, let's connect SimplePeer
@@ -412,8 +412,8 @@ export class GameScene extends Phaser.Scene implements CenterListener {
             this.switchLayoutMode();
         });
 
-        this.repositionCallback = this.reposition.bind(this);
-        window.addEventListener('resize', this.repositionCallback);
+        this.onResizeCallback = this.onResize.bind(this);
+        window.addEventListener('resize', this.onResizeCallback);
         this.reposition();
 
         // From now, this game scene will be notified of reposition events
@@ -636,7 +636,17 @@ export class GameScene extends Phaser.Scene implements CenterListener {
 
         //join room
         this.connectionPromise.then((connection: Connection) => {
-            connection.joinARoom(this.RoomId, this.startX, this.startY, PlayerAnimationNames.WalkDown, false).then((userPositions: MessageUserPositionInterface[]) => {
+            const camera = this.cameras.main;
+            connection.joinARoom(this.RoomId,
+                this.startX,
+                this.startY,
+                PlayerAnimationNames.WalkDown,
+                false, {
+                    left: camera.scrollX,
+                    top: camera.scrollY,
+                    right: camera.scrollX + camera.width,
+                    bottom: camera.scrollY + camera.height,
+                }).then((userPositions: MessageUserPositionInterface[]) => {
                 this.initUsersPosition(userPositions);
             });
 
@@ -747,7 +757,7 @@ export class GameScene extends Phaser.Scene implements CenterListener {
             this.simplePeer.unregister();
             this.scene.stop();
             this.scene.remove(this.scene.key);
-            window.removeEventListener('resize', this.repositionCallback);
+            window.removeEventListener('resize', this.onResizeCallback);
             this.scene.start(nextSceneKey.key, {
                 startLayerName: nextSceneKey.hash
             });
@@ -936,6 +946,19 @@ export class GameScene extends Phaser.Scene implements CenterListener {
         return mapUrlStart.substring(startPos, endPos);
     }
 
+    private onResize(): void {
+        this.reposition();
+
+        // Send new viewport to server
+        const camera = this.cameras.main;
+        this.connection.setViewport({
+            left: camera.scrollX,
+            top: camera.scrollY,
+            right: camera.scrollX + camera.width,
+            bottom: camera.scrollY + camera.height,
+        });
+    }
+
     private reposition(): void {
         this.presentationModeSprite.setY(this.game.renderer.height - 2);
         this.chatModeSprite.setY(this.game.renderer.height - 2);