diff --git a/OpenRA.Game/Traits/Waypoint.cs b/OpenRA.Game/Traits/Waypoint.cs
index c7afeae949..a0cf83becd 100644
--- a/OpenRA.Game/Traits/Waypoint.cs
+++ b/OpenRA.Game/Traits/Waypoint.cs
@@ -20,7 +20,7 @@ namespace OpenRA.Traits
 
 	class Waypoint : IOccupySpace, ISync, INotifyAddedToWorld, INotifyRemovedFromWorld
 	{
-		[Sync] CPos location;
+		[Sync] readonly CPos location;
 
 		public Waypoint(ActorInitializer init)
 		{
@@ -34,12 +34,14 @@ namespace OpenRA.Traits
 		public void AddedToWorld(Actor self)
 		{
 			self.World.ActorMap.AddInfluence(self, this);
+			self.World.ActorMap.AddPosition(self, this);
 			self.World.ScreenMap.Add(self);
 		}
 
 		public void RemovedFromWorld(Actor self)
 		{
 			self.World.ActorMap.RemoveInfluence(self, this);
+			self.World.ActorMap.RemovePosition(self, this);
 			self.World.ScreenMap.Remove(self);
 		}
 	}
diff --git a/OpenRA.Game/Traits/World/ActorMap.cs b/OpenRA.Game/Traits/World/ActorMap.cs
index af50470346..7a74294f40 100644
--- a/OpenRA.Game/Traits/World/ActorMap.cs
+++ b/OpenRA.Game/Traits/World/ActorMap.cs
@@ -10,15 +10,19 @@
 
 using System.Collections.Generic;
 using System.Linq;
+using OpenRA.FileFormats;
 using OpenRA.Traits;
 
 namespace OpenRA.Traits
 {
 	public enum SubCell { FullCell, TopLeft, TopRight, Center, BottomLeft, BottomRight }
 
-	class ActorMapInfo : ITraitInfo
+	public class ActorMapInfo : ITraitInfo
 	{
-		public object Create(ActorInitializer init) { return new ActorMap(init.world); }
+		[Desc("Size of partition bins (cells)")]
+		public readonly int BinSize = 10;
+
+		public object Create(ActorInitializer init) { return new ActorMap(init.world, this); }
 	}
 
 	public class ActorMap
@@ -30,13 +34,25 @@ namespace OpenRA.Traits
 			public Actor actor;
 		}
 
+		readonly ActorMapInfo info;
+		readonly Map map;
 		InfluenceNode[,] influence;
-		Map map;
 
-		public ActorMap(World world)
+		List<Actor>[] actors;
+		int rows, cols;
+
+		public ActorMap(World world, ActorMapInfo info)
 		{
+			this.info = info;
 			map = world.Map;
 			influence = new InfluenceNode[world.Map.MapSize.X, world.Map.MapSize.Y];
+
+			cols = world.Map.MapSize.X / info.BinSize + 1;
+			rows = world.Map.MapSize.Y / info.BinSize + 1;
+			actors = new List<Actor>[rows * cols];
+			for (var j = 0; j < rows; j++)
+				for (var i = 0; i < cols; i++)
+					actors[j * cols + i] = new List<Actor>();
 		}
 
 		public IEnumerable<Actor> GetUnitsAt(CPos a)
@@ -114,5 +130,25 @@ namespace OpenRA.Traits
 			if (influenceNode != null)
 				RemoveInfluenceInner(ref influenceNode.next, toRemove);
 		}
+
+		public void AddPosition(Actor a, IOccupySpace ios)
+		{
+			var pos = ios.CenterPosition;
+			var i = (pos.X / info.BinSize).Clamp(0, cols - 1);
+			var j = (pos.Y / info.BinSize).Clamp(0, rows - 1);
+			actors[j*cols + i].Add(a);
+		}
+
+		public void RemovePosition(Actor a, IOccupySpace ios)
+		{
+			foreach (var bin in actors)
+				bin.Remove(a);
+		}
+
+		public void UpdatePosition(Actor a, IOccupySpace ios)
+		{
+			RemovePosition(a, ios);
+			AddPosition(a, ios);
+		}
 	}
 }
diff --git a/OpenRA.Mods.RA/Air/Aircraft.cs b/OpenRA.Mods.RA/Air/Aircraft.cs
index c1baf48b51..ab88485cc6 100755
--- a/OpenRA.Mods.RA/Air/Aircraft.cs
+++ b/OpenRA.Mods.RA/Air/Aircraft.cs
@@ -106,7 +106,10 @@ namespace OpenRA.Mods.RA.Air
 			CenterPosition = pos;
 
 			if (self.IsInWorld)
+			{
 				self.World.ScreenMap.Update(self);
+				self.World.ActorMap.UpdatePosition(self, this);
+			}
 		}
 
 		// Changes position, but not altitude
@@ -116,12 +119,14 @@ namespace OpenRA.Mods.RA.Air
 		public void AddedToWorld(Actor self)
 		{
 			self.World.ActorMap.AddInfluence(self, this);
+			self.World.ActorMap.AddPosition(self, this);
 			self.World.ScreenMap.Add(self);
 		}
 
 		public void RemovedFromWorld(Actor self)
 		{
 			self.World.ActorMap.RemoveInfluence(self, this);
+			self.World.ActorMap.RemovePosition(self, this);
 			self.World.ScreenMap.Remove(self);
 		}
 
diff --git a/OpenRA.Mods.RA/Buildings/Building.cs b/OpenRA.Mods.RA/Buildings/Building.cs
index 0ec7af8b7a..60a3490dd5 100755
--- a/OpenRA.Mods.RA/Buildings/Building.cs
+++ b/OpenRA.Mods.RA/Buildings/Building.cs
@@ -161,12 +161,14 @@ namespace OpenRA.Mods.RA.Buildings
 		public void AddedToWorld(Actor self)
 		{
 			self.World.ActorMap.AddInfluence(self, this);
+			self.World.ActorMap.AddPosition(self, this);
 			self.World.ScreenMap.Add(self);
 		}
 
 		public void RemovedFromWorld(Actor self)
 		{
 			self.World.ActorMap.RemoveInfluence(self, this);
+			self.World.ActorMap.RemovePosition(self, this);
 			self.World.ScreenMap.Remove(self);
 		}
 	}
diff --git a/OpenRA.Mods.RA/Crate.cs b/OpenRA.Mods.RA/Crate.cs
index 68ba35bb26..2fdeb44bce 100644
--- a/OpenRA.Mods.RA/Crate.cs
+++ b/OpenRA.Mods.RA/Crate.cs
@@ -103,9 +103,7 @@ namespace OpenRA.Mods.RA
 
 		public void SetPosition(Actor self, CPos cell)
 		{
-			if (self.IsInWorld)
-				self.World.ActorMap.RemoveInfluence(self, this);
-
+			self.World.ActorMap.RemoveInfluence(self, this);
 			Location = cell;
 			CenterPosition = cell.CenterPosition;
 
@@ -117,6 +115,7 @@ namespace OpenRA.Mods.RA
 			if (self.IsInWorld)
 			{
 				self.World.ActorMap.AddInfluence(self, this);
+				self.World.ActorMap.UpdatePosition(self, this);
 				self.World.ScreenMap.Update(self);
 			}
 		}
@@ -129,12 +128,14 @@ namespace OpenRA.Mods.RA
 		public void AddedToWorld(Actor self)
 		{
 			self.World.ActorMap.AddInfluence(self, this);
+			self.World.ActorMap.AddPosition(self, this);
 			self.World.ScreenMap.Add(self);
 		}
 
 		public void RemovedFromWorld(Actor self)
 		{
 			self.World.ActorMap.RemoveInfluence(self, this);
+			self.World.ActorMap.RemovePosition(self, this);
 			self.World.ScreenMap.Remove(self);
 		}
 	}
diff --git a/OpenRA.Mods.RA/Husk.cs b/OpenRA.Mods.RA/Husk.cs
index 9e41fb64ca..2e9c0b0383 100644
--- a/OpenRA.Mods.RA/Husk.cs
+++ b/OpenRA.Mods.RA/Husk.cs
@@ -76,18 +76,21 @@ namespace OpenRA.Mods.RA
 			CenterPosition = pos;
 			TopLeft = pos.ToCPos();
 			self.World.ActorMap.AddInfluence(self, this);
+			self.World.ActorMap.UpdatePosition(self, this);
 			self.World.ScreenMap.Update(self);
 		}
 
 		public void AddedToWorld(Actor self)
 		{
 			self.World.ActorMap.AddInfluence(self, this);
+			self.World.ActorMap.AddPosition(self, this);
 			self.World.ScreenMap.Add(self);
 		}
 
 		public void RemovedFromWorld(Actor self)
 		{
 			self.World.ActorMap.RemoveInfluence(self, this);
+			self.World.ActorMap.RemovePosition(self, this);
 			self.World.ScreenMap.Remove(self);
 		}
 	}
diff --git a/OpenRA.Mods.RA/Mine.cs b/OpenRA.Mods.RA/Mine.cs
index f42264d4a8..aa45da5d14 100644
--- a/OpenRA.Mods.RA/Mine.cs
+++ b/OpenRA.Mods.RA/Mine.cs
@@ -66,12 +66,14 @@ namespace OpenRA.Mods.RA
 		public void AddedToWorld(Actor self)
 		{
 			self.World.ActorMap.AddInfluence(self, this);
+			self.World.ActorMap.AddPosition(self, this);
 			self.World.ScreenMap.Add(self);
 		}
 
 		public void RemovedFromWorld(Actor self)
 		{
 			self.World.ActorMap.RemoveInfluence(self, this);
+			self.World.ActorMap.RemovePosition(self, this);
 			self.World.ScreenMap.Remove(self);
 		}
 	}
diff --git a/OpenRA.Mods.RA/Move/Mobile.cs b/OpenRA.Mods.RA/Move/Mobile.cs
index 1679654e42..fb315d6267 100755
--- a/OpenRA.Mods.RA/Move/Mobile.cs
+++ b/OpenRA.Mods.RA/Move/Mobile.cs
@@ -232,18 +232,23 @@ namespace OpenRA.Mods.RA.Move
 		{
 			CenterPosition = pos;
 			if (self.IsInWorld)
+			{
 				self.World.ScreenMap.Update(self);
+				self.World.ActorMap.UpdatePosition(self, this);
+			}
 		}
 
 		public void AddedToWorld(Actor self)
 		{
 			self.World.ActorMap.AddInfluence(self, this);
+			self.World.ActorMap.AddPosition(self, this);
 			self.World.ScreenMap.Add(self);
 		}
 
 		public void RemovedFromWorld(Actor self)
 		{
 			self.World.ActorMap.RemoveInfluence(self, this);
+			self.World.ActorMap.RemovePosition(self, this);
 			self.World.ScreenMap.Remove(self);
 		}