diff --git a/proto/cityio/service/v1/map.proto b/proto/cityio/service/v1/map.proto
index 6429a7b..1d62b9b 100644
--- a/proto/cityio/service/v1/map.proto
+++ b/proto/cityio/service/v1/map.proto
@@ -30,27 +30,36 @@ message GetTileResponse {
 
 message GetTerrainRequest {}
 
-// GetTerrainResponse carries the whole map in one call.
+// VisibleTerrain is the ground a player can see right now.
 //
-// Each plane is packed one byte per tile in row-major order, so the value for
-// (x, y) is at index y * width + x. At the current map size that is about 5 KB
-// per plane — small enough that chunking or viewport queries would cost more
-// than they save, and it lets the client cache the world for the session.
+// Vision is ephemeral: it comes from cities, from armies while they stand
+// somewhere, and from structures held against an enemy. Tiles therefore leave
+// this set as often as they enter it, so it is always sent whole rather than as
+// a reveal-only delta — replacing the set outright is the only way client and
+// server cannot disagree about what is still lit.
 //
-// Terrain is generated by the server from `seed` and does not change, so this
-// response is stable for the lifetime of a world.
+// Tiles are addressed by row-major index (y * width + x). Each plane holds one
+// byte per entry of `indices`, in the same order.
+message VisibleTerrain {
+  repeated int32 indices = 1;
+  bytes terrain = 2; // cityio.entity.v1.TerrainType
+  bytes relief = 3; // cityio.entity.v1.ReliefType
+  bytes feature = 4; // cityio.entity.v1.FeatureType
+  bytes special = 5; // cityio.entity.v1.SpecialType
+  // rivers holds a 6-bit mask per tile: bit i means a river continues toward
+  // neighbour i. Both tiles either side of a step carry the reciprocal bit, so
+  // each renders its own half and rivers occupy no tile of their own.
+  bytes rivers = 6;
+}
+
+// GetTerrainResponse bootstraps a client with the map's dimensions and whatever
+// ground it can currently see. Everything else is unknown, and stays unknown
+// until something of the player's is watching it.
 message GetTerrainResponse {
   int32 width = 1;
   int32 height = 2;
   int64 seed = 3;
-  bytes terrain = 4; // cityio.entity.v1.TerrainType per tile
-  bytes relief = 5; // cityio.entity.v1.ReliefType per tile
-  bytes feature = 6; // cityio.entity.v1.FeatureType per tile
-  bytes special = 7; // cityio.entity.v1.SpecialType per tile
-  // rivers holds a 6-bit mask per tile: bit i means a river continues toward
-  // neighbour i. Both tiles either side of a step carry the reciprocal bit, so
-  // each renders its own half and rivers occupy no tile of their own.
-  bytes rivers = 8;
+  VisibleTerrain visible = 4;
 }
 
 // MapService serves world snapshots read from the persistence layer.
diff --git a/proto/cityio/service/v1/user.proto b/proto/cityio/service/v1/user.proto
index bedb30d..be609de 100644
--- a/proto/cityio/service/v1/user.proto
+++ b/proto/cityio/service/v1/user.proto
@@ -5,6 +5,7 @@ package cityio.service.v1;
 import "cityio/entity/v1/common.proto";
 import "cityio/entity/v1/user.proto";
 import "cityio/entity/v1/bag.proto";
+import "cityio/service/v1/map.proto";
 
 message RegisterRequest {
   string email = 1;
@@ -42,6 +43,10 @@ message StreamStateRequest {}
 // StreamStateResponse wraps an EntityBag pushed to a client whenever state changes.
 message StreamStateResponse {
   cityio.entity.v1.EntityBag entities = 1;
+  // The player's currently visible ground, sent whole whenever it changes and
+  // omitted when it has not. Absent on most ticks, since vision only moves when
+  // a city, army or watchtower does.
+  optional VisibleTerrain visible_terrain = 2;
 }
 
 // UserService manages player accounts and the per-user resource stream.
diff --git a/src/lib/game/world/index.ts b/src/lib/game/world/index.ts
index b187edd..2cb8115 100644
--- a/src/lib/game/world/index.ts
+++ b/src/lib/game/world/index.ts
@@ -18,6 +18,55 @@ export interface WorldMap {
   special: Uint8Array;
   /** 6-bit mask per tile: bit i means a river continues toward neighbor i. */
   rivers: Uint8Array;
+  /**
+   * 1 where the player can see the ground right now. Vision is ephemeral — it
+   * lasts only while a city, army or held structure is watching — so tiles
+   * leave this set as readily as they enter it, and the planes above are only
+   * meaningful where it is set.
+   */
+  visible: Uint8Array;
+}
+
+export function emptyWorld(w: number, h: number, seed: bigint): WorldMap {
+  const n = w * h;
+  return {
+    w,
+    h,
+    seed,
+    terrain: new Uint8Array(n),
+    relief: new Uint8Array(n),
+    feature: new Uint8Array(n),
+    special: new Uint8Array(n),
+    rivers: new Uint8Array(n),
+    visible: new Uint8Array(n)
+  };
+}
+
+/**
+ * Replace what the player can see with the set the server just sent.
+ *
+ * The whole set arrives every time rather than a reveal-only delta, because
+ * losing sight of ground is as common as gaining it. Clearing first is what
+ * makes a tile actually go dark when the army watching it walks away.
+ */
+export function applyVisibleTerrain(world: WorldMap, v: { indices: number[]; terrain: Uint8Array; relief: Uint8Array; feature: Uint8Array; special: Uint8Array; rivers: Uint8Array }): void {
+  world.terrain.fill(0);
+  world.relief.fill(0);
+  world.feature.fill(0);
+  world.special.fill(0);
+  world.rivers.fill(0);
+  world.visible.fill(0);
+
+  for (let k = 0; k < v.indices.length; k++) {
+    const i = v.indices[k];
+    if (i < 0 || i >= world.visible.length) continue;
+    world.terrain[i] = v.terrain[k];
+    world.relief[i] = v.relief[k];
+    world.feature[i] = v.feature[k];
+    world.special[i] = v.special[k];
+    world.rivers[i] = v.rivers[k];
+    world.visible[i] = 1;
+  }
 }
 
 export const isWater = (t: TerrainType) => t >= TerrainType.DEEP_OCEAN && t <= TerrainType.LAKE;
diff --git a/src/lib/gen/cityio/service/v1/map_pb.ts b/src/lib/gen/cityio/service/v1/map_pb.ts
index 8822def..80b2bd4 100644
--- a/src/lib/gen/cityio/service/v1/map_pb.ts
+++ b/src/lib/gen/cityio/service/v1/map_pb.ts
@@ -14,7 +14,7 @@ import type { Message } from "@bufbuild/protobuf";
  * Describes the file cityio/service/v1/map.proto.
  */
 export const file_cityio_service_v1_map: GenFile = /*@__PURE__*/
-  fileDesc("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", [file_cityio_entity_v1_common, file_cityio_entity_v1_bag]);
+  fileDesc("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", [file_cityio_entity_v1_common, file_cityio_entity_v1_bag]);
 
 /**
  * @generated from message cityio.service.v1.GetMapRequest
@@ -138,59 +138,50 @@ export const GetTerrainRequestSchema: GenMessage<GetTerrainRequest> = /*@__PURE_
   messageDesc(file_cityio_service_v1_map, 5);
 
 /**
- * GetTerrainResponse carries the whole map in one call.
+ * VisibleTerrain is the ground a player can see right now.
  *
- * Each plane is packed one byte per tile in row-major order, so the value for
- * (x, y) is at index y * width + x. At the current map size that is about 5 KB
- * per plane — small enough that chunking or viewport queries would cost more
- * than they save, and it lets the client cache the world for the session.
+ * Vision is ephemeral: it comes from cities, from armies while they stand
+ * somewhere, and from structures held against an enemy. Tiles therefore leave
+ * this set as often as they enter it, so it is always sent whole rather than as
+ * a reveal-only delta — replacing the set outright is the only way client and
+ * server cannot disagree about what is still lit.
  *
- * Terrain is generated by the server from `seed` and does not change, so this
- * response is stable for the lifetime of a world.
+ * Tiles are addressed by row-major index (y * width + x). Each plane holds one
+ * byte per entry of `indices`, in the same order.
  *
- * @generated from message cityio.service.v1.GetTerrainResponse
+ * @generated from message cityio.service.v1.VisibleTerrain
  */
-export type GetTerrainResponse = Message<"cityio.service.v1.GetTerrainResponse"> & {
-  /**
-   * @generated from field: int32 width = 1;
-   */
-  width: number;
-
-  /**
-   * @generated from field: int32 height = 2;
-   */
-  height: number;
-
+export type VisibleTerrain = Message<"cityio.service.v1.VisibleTerrain"> & {
   /**
-   * @generated from field: int64 seed = 3;
+   * @generated from field: repeated int32 indices = 1;
    */
-  seed: bigint;
+  indices: number[];
 
   /**
-   * cityio.entity.v1.TerrainType per tile
+   * cityio.entity.v1.TerrainType
    *
-   * @generated from field: bytes terrain = 4;
+   * @generated from field: bytes terrain = 2;
    */
   terrain: Uint8Array;
 
   /**
-   * cityio.entity.v1.ReliefType per tile
+   * cityio.entity.v1.ReliefType
    *
-   * @generated from field: bytes relief = 5;
+   * @generated from field: bytes relief = 3;
    */
   relief: Uint8Array;
 
   /**
-   * cityio.entity.v1.FeatureType per tile
+   * cityio.entity.v1.FeatureType
    *
-   * @generated from field: bytes feature = 6;
+   * @generated from field: bytes feature = 4;
    */
   feature: Uint8Array;
 
   /**
-   * cityio.entity.v1.SpecialType per tile
+   * cityio.entity.v1.SpecialType
    *
-   * @generated from field: bytes special = 7;
+   * @generated from field: bytes special = 5;
    */
   special: Uint8Array;
 
@@ -199,17 +190,53 @@ export type GetTerrainResponse = Message<"cityio.service.v1.GetTerrainResponse">
    * neighbour i. Both tiles either side of a step carry the reciprocal bit, so
    * each renders its own half and rivers occupy no tile of their own.
    *
-   * @generated from field: bytes rivers = 8;
+   * @generated from field: bytes rivers = 6;
    */
   rivers: Uint8Array;
 };
 
+/**
+ * Describes the message cityio.service.v1.VisibleTerrain.
+ * Use `create(VisibleTerrainSchema)` to create a new message.
+ */
+export const VisibleTerrainSchema: GenMessage<VisibleTerrain> = /*@__PURE__*/
+  messageDesc(file_cityio_service_v1_map, 6);
+
+/**
+ * GetTerrainResponse bootstraps a client with the map's dimensions and whatever
+ * ground it can currently see. Everything else is unknown, and stays unknown
+ * until something of the player's is watching it.
+ *
+ * @generated from message cityio.service.v1.GetTerrainResponse
+ */
+export type GetTerrainResponse = Message<"cityio.service.v1.GetTerrainResponse"> & {
+  /**
+   * @generated from field: int32 width = 1;
+   */
+  width: number;
+
+  /**
+   * @generated from field: int32 height = 2;
+   */
+  height: number;
+
+  /**
+   * @generated from field: int64 seed = 3;
+   */
+  seed: bigint;
+
+  /**
+   * @generated from field: cityio.service.v1.VisibleTerrain visible = 4;
+   */
+  visible?: VisibleTerrain | undefined;
+};
+
 /**
  * Describes the message cityio.service.v1.GetTerrainResponse.
  * Use `create(GetTerrainResponseSchema)` to create a new message.
  */
 export const GetTerrainResponseSchema: GenMessage<GetTerrainResponse> = /*@__PURE__*/
-  messageDesc(file_cityio_service_v1_map, 6);
+  messageDesc(file_cityio_service_v1_map, 7);
 
 /**
  * MapService serves world snapshots read from the persistence layer.
diff --git a/src/lib/gen/cityio/service/v1/user_pb.ts b/src/lib/gen/cityio/service/v1/user_pb.ts
index 41877a9..45c03cd 100644
--- a/src/lib/gen/cityio/service/v1/user_pb.ts
+++ b/src/lib/gen/cityio/service/v1/user_pb.ts
@@ -10,13 +10,15 @@ import type { User } from "../../entity/v1/user_pb";
 import { file_cityio_entity_v1_user } from "../../entity/v1/user_pb";
 import type { EntityBag } from "../../entity/v1/bag_pb";
 import { file_cityio_entity_v1_bag } from "../../entity/v1/bag_pb";
+import type { VisibleTerrain } from "./map_pb";
+import { file_cityio_service_v1_map } from "./map_pb";
 import type { Message } from "@bufbuild/protobuf";
 
 /**
  * Describes the file cityio/service/v1/user.proto.
  */
 export const file_cityio_service_v1_user: GenFile = /*@__PURE__*/
-  fileDesc("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", [file_cityio_entity_v1_common, file_cityio_entity_v1_user, file_cityio_entity_v1_bag]);
+  fileDesc("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", [file_cityio_entity_v1_common, file_cityio_entity_v1_user, file_cityio_entity_v1_bag, file_cityio_service_v1_map]);
 
 /**
  * @generated from message cityio.service.v1.RegisterRequest
@@ -198,6 +200,15 @@ export type StreamStateResponse = Message<"cityio.service.v1.StreamStateResponse
    * @generated from field: cityio.entity.v1.EntityBag entities = 1;
    */
   entities?: EntityBag | undefined;
+
+  /**
+   * The player's currently visible ground, sent whole whenever it changes and
+   * omitted when it has not. Absent on most ticks, since vision only moves when
+   * a city, army or watchtower does.
+   *
+   * @generated from field: optional cityio.service.v1.VisibleTerrain visible_terrain = 2;
+   */
+  visibleTerrain?: VisibleTerrain | undefined;
 };
 
 /**
diff --git a/src/routes/game/+layout.svelte b/src/routes/game/+layout.svelte
index f5b1c93..5851865 100644
--- a/src/routes/game/+layout.svelte
+++ b/src/routes/game/+layout.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
   import { mapClient, userClient, configClient } from '$lib/api/client';
   import { token, buildings as buildingsStore, capital, cities as citiesStore, food, foodIncomePerHour, foodUpkeepPerHour, gameConfig, gold, mapCenter, userId, world } from '$lib/stores';
+  import { applyVisibleTerrain, emptyWorld } from '$lib/game/world';
   import { ratePerHour } from '$lib/game/rates';
   import { isTokenValid, handleUnauthenticated } from '$lib/session';
   import { Code, ConnectError } from '@connectrpc/connect';
@@ -43,12 +44,15 @@
     }
   };
 
-  // Terrain is generated and owned by the server. It never changes, so this is
-  // fetched once and cached for the session.
+  // Terrain is generated and owned by the server, and only the ground the
+  // player can currently see is sent. Vision is ephemeral, so the stream keeps
+  // this up to date as cities, armies and held structures move.
   const loadTerrain = async (): Promise<boolean> => {
     try {
       const t = await mapClient.getTerrain({});
-      world.set({ w: t.width, h: t.height, seed: t.seed, terrain: t.terrain, relief: t.relief, feature: t.feature, special: t.special, rivers: t.rivers });
+      const w = emptyWorld(t.width, t.height, t.seed);
+      if (t.visible) applyVisibleTerrain(w, t.visible);
+      world.set(w);
       return true;
     } catch (err) {
       if (err instanceof ConnectError && err.code === Code.Unauthenticated) return false;
@@ -88,6 +92,15 @@
     while (!signal.aborted) {
       try {
         for await (const state of userClient.streamState({}, { signal })) {
+          // Vision moved: replace what the player can see. Absent on most
+          // ticks, since only a city, army or watchtower moving changes it.
+          if (state.visibleTerrain) {
+            world.update((w) => {
+              if (w) applyVisibleTerrain(w, state.visibleTerrain!);
+              return w;
+            });
+          }
+
           const bag = state.entities;
           if (!bag) continue;
 
diff --git a/src/routes/game/+page.svelte b/src/routes/game/+page.svelte
index ef5addb..b07d7b5 100644
--- a/src/routes/game/+page.svelte
+++ b/src/routes/game/+page.svelte
@@ -8,7 +8,7 @@
   import { S, HEX_H, HEX_VERTS, hexToPixel, pixelToHex, tileKey, hexNeighbors } from '$lib/game/hex';
   import { varyColor } from '$lib/game/colors';
   import { ANCHOR_X, ANCHOR_Y } from '$lib/game/render/geometry';
-  import { featureTexture, groundTexture, reliefTexture, riverTexture, specialTexture } from '$lib/game/render/terrainTex';
+  import { featureTexture, groundTexture, reliefTexture, riverTexture, shroudTexture, specialTexture } from '$lib/game/render/terrainTex';
   import { buildingTexture } from '$lib/game/render/buildingTex';
   import { describeTile, Feature, Relief, Special, Terrain, SPECIAL_NAME } from '$lib/game/world';
   import { ratePerHour, fmtPerHour, durationSeconds } from '$lib/game/rates';
@@ -23,8 +23,6 @@
   const MIN_ZOOM = 0.4;
   const MAX_ZOOM = 3;
   const CLICK_DIST = 5;
-  /** Cool desaturating multiply applied to terrain outside vision range. */
-  const FOG_TINT = 0x63758a;
 
   // ── pixi state ──────────────────────────────────────────
   let app: Application;
@@ -182,6 +180,10 @@
       rebuildTiles();
     });
   };
+  // Vision moved, so the set of lit tiles changed — redraw. The store is
+  // updated in place, but Svelte notifies on every set regardless of identity.
+  $: if ($world) scheduleRender();
+
   $: if ($cities || $buildings) {
     buildLookup();
     // Immediately hide construction overlays for finished/removed constructions
@@ -220,20 +222,23 @@
   };
 
   // ── visibility (fog of war) ─────────────────────────────
-  const getVisDist = (col: number, row: number): number => {
-    let min = Infinity;
-    for (const city of myCities) {
-      if (!city.start) continue;
-      const sx = city.start.x,
-        sy = city.start.y,
-        s = city.size;
-      const dx = Math.max(sx - col, col - (sx + s - 1), 0);
-      const dy = Math.max(sy - row, row - (sy + s - 1), 0);
-      min = Math.min(min, Math.max(dx, dy));
-    }
-    return min;
+  // The server decides visibility and sends only what it grants, so ask the
+  // world rather than recomputing a distance the client would get wrong —
+  // armies grant vision too, and the client does not track their radius.
+  const tileIsVisible = (col: number, row: number): boolean => {
+    const w = $world;
+    if (!w || col < 0 || row < 0 || col >= w.w || row >= w.h) return false;
+    return w.visible[row * w.w + col] === 1;
+  };
+
+  /** Terrain description for the selected tile, e.g. "Grassland · Hills · Forest". */
+  const tileTerrain = (col: number, row: number): string => {
+    const w = $world;
+    if (!w || !tileIsVisible(col, row)) return '';
+    return describeTile(w, col, row);
   };
 
+
   const getCenter = () => {
     if (!cont) return { x: 0, y: 0 };
     return pixelToHex((-cont.x + cw / 2) / cont.scale.x, (-cont.y + ch / 2) / cont.scale.y);
@@ -512,37 +517,38 @@
     cont.addChild(tc);
     loaded.set(k, tc);
 
-    const dist = myCities.length > 0 ? getVisDist(col, row) : 0;
-    const inFog = dist > $gameConfig.visionRadius;
     const i = row * w.w + col;
-
-    // Terrain is drawn everywhere; outside vision it is desaturated rather than
-    // blacked out. Nothing leaks — the server filters entities by vision, so a
-    // fogged tile has no city or building to reveal in the first place.
-    const tint = inFog ? FOG_TINT : varyColor(0xffffff, col, row, 10);
+    // The server decides what is visible and sends only that ground. Vision is
+    // ephemeral, so a tile goes dark again the moment nothing of the player's
+    // is watching it — there is no remembered terrain to fall back on.
+    const inFog = w.visible[i] !== 1;
 
     const layer = (texture: Texture) => {
       const spr = new Sprite(texture);
       spr.anchor.set(ANCHOR_X, ANCHOR_Y);
-      spr.tint = tint;
+      spr.tint = varyColor(0xffffff, col, row, 10);
       tc.addChild(spr);
       return spr;
     };
 
-    const ground = w.terrain[i] as Terrain;
-    // Peaks are capped and conifers turn boreal on cold ground. Derived from
-    // the ground plane rather than a shipped temperature field.
-    const cold = ground === Terrain.TUNDRA || ground === Terrain.SNOW;
-    layer(groundTexture(ground, col, row));
-
-    if (w.rivers[i]) layer(riverTexture(w.rivers[i], col, row));
-    if (w.relief[i] !== Relief.FLAT) layer(reliefTexture(w.relief[i] as Relief, col, row, cold));
-    if (w.feature[i] !== Feature.UNSPECIFIED) layer(featureTexture(w.feature[i] as Feature, col, row, cold));
-    if (w.special[i] && !inFog) layer(specialTexture(w.special[i] as Special));
-
-    if (td?.building) {
-      const bt = buildingTexture(td.building.type);
-      if (bt) layer(bt);
+    if (inFog) {
+      layer(shroudTexture());
+    } else {
+      const ground = w.terrain[i] as Terrain;
+      // Peaks are capped and conifers turn boreal on cold ground. Derived from
+      // the ground plane rather than a shipped temperature field.
+      const cold = ground === Terrain.TUNDRA || ground === Terrain.SNOW;
+      layer(groundTexture(ground, col, row));
+
+      if (w.rivers[i]) layer(riverTexture(w.rivers[i], col, row));
+      if (w.relief[i] !== Relief.FLAT) layer(reliefTexture(w.relief[i] as Relief, col, row, cold));
+      if (w.feature[i] !== Feature.UNSPECIFIED) layer(featureTexture(w.feature[i] as Feature, col, row, cold));
+      if (w.special[i]) layer(specialTexture(w.special[i] as Special));
+
+      if (td?.building) {
+        const bt = buildingTexture(td.building.type);
+        if (bt) layer(bt);
+      }
     }
 
     // Construction-in-progress overlay
@@ -582,8 +588,16 @@
         }
       }
 
-      // Visibility edge glow
-      if (dist >= $gameConfig.visionRadius - 1) {
+      // Visibility edge glow — a lit tile with an unlit neighbour is the edge
+      // of what the player can currently see.
+      let onVisionEdge = false;
+      for (const [nc, nr] of hexNeighbors(col, row)) {
+        if (nc < 0 || nr < 0 || nc >= w.w || nr >= w.h || w.visible[nr * w.w + nc] !== 1) {
+          onVisionEdge = true;
+          break;
+        }
+      }
+      if (onVisionEdge) {
         g.poly(HEX_VERTS);
         g.stroke({ color: 0x40a0b0, width: 1.5, alpha: 0.2 });
         hasOverlay = true;
@@ -978,7 +992,15 @@
       <div class="pointer-events-auto space-y-3 rounded-lg bg-gray-900/85 p-3 backdrop-blur-sm" transition:fly={{ x: 16, duration: 200 }}>
         <!-- Header -->
         <div class="flex items-center justify-between">
-          <span class="rounded-md bg-white/[0.06] px-2 py-0.5 font-mono text-[10px] text-gray-500">{sel.x}, {sel.y}</span>
+          <span class="flex items-center gap-2">
+            <span class="rounded-md bg-white/[0.06] px-2 py-0.5 font-mono text-[10px] text-gray-500">{sel.x}, {sel.y}</span>
+            {#if tileTerrain(sel.x, sel.y)}
+              <span class="text-[11px] text-gray-400">{tileTerrain(sel.x, sel.y)}</span>
+            {/if}
+            {#if tileIsVisible(sel.x, sel.y) && $world && $world.special[sel.y * $world.w + sel.x]}
+              <span class="rounded-md bg-amber-500/15 px-1.5 py-0.5 text-[10px] text-amber-300">{SPECIAL_NAME[$world.special[sel.y * $world.w + sel.x]]}</span>
+            {/if}
+          </span>
           <button
             aria-label="Close"
             class="flex h-5 w-5 items-center justify-center rounded-lg text-gray-600 transition-colors duration-150 hover:bg-white/[0.06] hover:text-gray-300"
@@ -1198,7 +1220,7 @@
         {:else if !sel.city}
           <!-- Empty tile message -->
           <div class="py-3 text-center text-xs text-gray-600">
-            {myCities.length > 0 && getVisDist(sel.x, sel.y) > $gameConfig.visionRadius ? 'Beyond visibility range' : 'No structures on this tile'}
+            {tileIsVisible(sel.x, sel.y) ? 'No structures on this tile' : 'Nothing of yours is watching this tile'}
           </div>
         {/if}
       </div>