diff --git a/OpenRA.Game/Graphics/Minimap.cs b/OpenRA.Game/Graphics/Minimap.cs
index 24141ac9f2..d0ec1b86fd 100644
--- a/OpenRA.Game/Graphics/Minimap.cs
+++ b/OpenRA.Game/Graphics/Minimap.cs
@@ -32,6 +32,8 @@ namespace OpenRA.Graphics
 			var bitmapData = terrain.LockBits(terrain.Bounds(),
 				ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
 
+			var mapTiles = map.MapTiles.Value;
+
 			unsafe
 			{
 				int* c = (int*)bitmapData.Scan0;
@@ -41,11 +43,9 @@ namespace OpenRA.Graphics
 					{
 						var mapX = x + map.Bounds.Left;
 						var mapY = y + map.Bounds.Top;
-						var type = tileset.GetTerrainType(map.MapTiles.Value[mapX, mapY]);
-						if (!tileset.Terrain.ContainsKey(type))
-							throw new InvalidDataException("Tileset {0} lacks terraintype {1}".F(tileset.Id, type));
+						var type = tileset.GetTerrainInfo(mapTiles[mapX, mapY]);
 
-						*(c + (y * bitmapData.Stride >> 2) + x) = tileset.Terrain[type].Color.ToArgb();
+						*(c + (y * bitmapData.Stride >> 2) + x) = type.Color.ToArgb();
 					}
 			}
 
@@ -80,7 +80,7 @@ namespace OpenRA.Graphics
 						if (res == null)
 							continue;
 
-						*(c + (y * bitmapData.Stride >> 2) + x) = tileset.Terrain[res].Color.ToArgb();
+						*(c + (y * bitmapData.Stride >> 2) + x) = tileset[tileset.GetTerrainIndex(res)].Color.ToArgb();
 					}
 			}
 
@@ -107,9 +107,9 @@ namespace OpenRA.Graphics
 						var mapX = x + map.Bounds.Left;
 						var mapY = y + map.Bounds.Top;
 						var custom = map.CustomTerrain[mapX, mapY];
-						if (custom == null)
+						if (custom == -1)
 							continue;
-						*(c + (y * bitmapData.Stride >> 2) + x) = world.TileSet.Terrain[custom].Color.ToArgb();
+						*(c + (y * bitmapData.Stride >> 2) + x) = world.TileSet[custom].Color.ToArgb();
 					}
 			}
 
diff --git a/OpenRA.Game/Map/Map.cs b/OpenRA.Game/Map/Map.cs
index c7a23519f5..1d99ab4512 100644
--- a/OpenRA.Game/Map/Map.cs
+++ b/OpenRA.Game/Map/Map.cs
@@ -111,7 +111,7 @@ namespace OpenRA
 
 		[FieldLoader.Ignore] public Lazy<TileReference<ushort, byte>[,]> MapTiles;
 		[FieldLoader.Ignore] public Lazy<TileReference<byte, byte>[,]> MapResources;
-		[FieldLoader.Ignore] public string[,] CustomTerrain;
+		[FieldLoader.Ignore] public int[,] CustomTerrain;
 
 		[FieldLoader.Ignore] Lazy<Ruleset> rules;
 		public Ruleset Rules { get { return rules != null ? rules.Value : null; } }
@@ -228,7 +228,10 @@ namespace OpenRA
 			NotificationDefinitions = MiniYaml.NodesOrEmpty(yaml, "Notifications");
 			TranslationDefinitions = MiniYaml.NodesOrEmpty(yaml, "Translations");
 
-			CustomTerrain = new string[MapSize.X, MapSize.Y];
+			CustomTerrain = new int[MapSize.X, MapSize.Y];
+			for (var x = 0; x < MapSize.X; x++)
+				for (var y = 0; y < MapSize.Y; y++)
+					CustomTerrain[x, y] = -1;
 
 			MapTiles = Exts.Lazy(() => LoadMapTiles());
 			MapResources = Exts.Lazy(() => LoadResourceTiles());
@@ -529,7 +532,7 @@ namespace OpenRA
 					var template = tileset.Templates[tr.Type];
 					if (!template.PickAny)
 						continue;
-					tr.Index = (byte)r.Next(0, template.Tiles.Count);
+					tr.Index = (byte)r.Next(0, template.TilesCount);
 					MapTiles.Value[i, j] = tr;
 				}
 			}
diff --git a/OpenRA.Game/Map/TileSet.cs b/OpenRA.Game/Map/TileSet.cs
index 082cd3d49b..ca82e15e3e 100644
--- a/OpenRA.Game/Map/TileSet.cs
+++ b/OpenRA.Game/Map/TileSet.cs
@@ -11,6 +11,7 @@
 using System;
 using System.Collections.Generic;
 using System.Drawing;
+using System.IO;
 using System.Linq;
 using System.Reflection;
 using OpenRA.Graphics;
@@ -41,29 +42,81 @@ namespace OpenRA
 		public readonly bool PickAny;
 		public readonly string Category;
 
-		[FieldLoader.LoadUsing("LoadTiles")]
-		public readonly Dictionary<byte, string> Tiles = new Dictionary<byte, string>();
+		int[] tiles;
 
-		public TileTemplate() { }
-		public TileTemplate(MiniYaml my) { FieldLoader.Load(this, my); }
-
-		public TileTemplate(ushort id, string image, int2 size)
+		public TileTemplate(ushort id, string image, int2 size, int[] tiles)
 		{
 			this.Id = id;
 			this.Image = image;
 			this.Size = size;
+			this.tiles = tiles;
 		}
 
-		static object LoadTiles(MiniYaml y)
+		public TileTemplate(TileSet tileSet, MiniYaml my)
 		{
-			return y.ToDictionary()["Tiles"].ToDictionary(
-				name => byte.Parse(name),
-				my => my.Value);
+			FieldLoader.Load(this, my);
+
+			tiles = LoadTiles(tileSet, my);
+		}
+
+		int[] LoadTiles(TileSet tileSet, MiniYaml y)
+		{
+			var nodes = y.ToDictionary()["Tiles"].Nodes;
+
+			if (!PickAny)
+			{
+				var tiles = new int[Size.X * Size.Y];
+
+				for (var i = 0; i < tiles.Length; i++)
+					tiles[i] = -1;
+
+				foreach (var node in nodes)
+				{
+					int key;
+					if (!int.TryParse(node.Key, out key) || key < 0 || key >= tiles.Length)
+						throw new InvalidDataException("Invalid tile key '{0}' on template '{1}' of tileset '{2}'.".F(node.Key, Id, tileSet.Id));
+
+					tiles[key] = tileSet.GetTerrainIndex(node.Value.Value);
+				}
+
+				return tiles;
+			}
+			else
+			{
+				var tiles = new int[nodes.Count];
+				var i = 0;
+
+				foreach (var node in nodes)
+				{
+					int key;
+					if (!int.TryParse(node.Key, out key) || key != i++)
+						throw new InvalidDataException("Invalid tile key '{0}' on template '{1}' of tileset '{2}'.".F(node.Key, Id, tileSet.Id));
+
+					tiles[key] = tileSet.GetTerrainIndex(node.Value.Value);
+				}
+
+				return tiles;
+			}
 		}
 
 		static readonly string[] Fields = { "Id", "Image", "Frames", "Size", "PickAny" };
 
-		public MiniYaml Save()
+		public int this[int index]
+		{
+			get { return tiles[index]; }
+		}
+
+		public bool Contains(int index)
+		{
+			return index >= 0 && index < tiles.Length;
+		}
+
+		public int TilesCount
+		{
+			get { return tiles.Length; }
+		}
+
+		public MiniYaml Save(TileSet tileSet)
 		{
 			var root = new List<MiniYamlNode>();
 			foreach (var field in Fields)
@@ -76,7 +129,7 @@ namespace OpenRA
 			}
 
 			root.Add(new MiniYamlNode("Tiles", null,
-				Tiles.Select(x => new MiniYamlNode(x.Key.ToString(), x.Value)).ToList()));
+				tiles.Select((terrainTypeIndex, templateIndex) => new MiniYamlNode(templateIndex.ToString(), tileSet[terrainTypeIndex].Type)).ToList()));
 
 			return new MiniYaml(null, root);
 		}
@@ -91,10 +144,13 @@ namespace OpenRA
 		public readonly string PlayerPalette;
 		public readonly string[] Extensions;
 		public readonly int WaterPaletteRotationBase = 0x60; 
-		public readonly Dictionary<string, TerrainTypeInfo> Terrain = new Dictionary<string, TerrainTypeInfo>();
 		public readonly Dictionary<ushort, TileTemplate> Templates = new Dictionary<ushort, TileTemplate>();
 		public readonly string[] EditorTemplateOrder;
 
+		readonly TerrainTypeInfo[] terrainInfo;
+		readonly Dictionary<string, int> terrainIndexByType = new Dictionary<string, int>();
+		readonly int defaultWalkableTerrainIndex;
+
 		static readonly string[] Fields = { "Name", "Id", "SheetSize", "Palette", "Extensions" };
 
 		public TileSet(ModData modData, string filepath)
@@ -105,20 +161,83 @@ namespace OpenRA
 			FieldLoader.Load(this, yaml["General"]);
 
 			// TerrainTypes
-			Terrain = yaml["Terrain"].ToDictionary().Values
-				.Select(y => new TerrainTypeInfo(y)).ToDictionary(t => t.Type);
+			terrainInfo = yaml["Terrain"].ToDictionary().Values
+				.Select(y => new TerrainTypeInfo(y))
+				.OrderBy(tt => tt.Type)
+				.ToArray();
+			for (var i = 0; i < terrainInfo.Length; i++)
+			{
+				var tt = terrainInfo[i].Type;
+
+				if (terrainIndexByType.ContainsKey(tt))
+					throw new InvalidDataException("Duplicate terrain type '{0}' in '{1}'.".F(tt, filepath));
+
+				terrainIndexByType.Add(tt, i);
+			}
+
+			defaultWalkableTerrainIndex = GetTerrainIndex("Clear");
 
 			// Templates
 			Templates = yaml["Templates"].ToDictionary().Values
-				.Select(y => new TileTemplate(y)).ToDictionary(t => t.Id);
+				.Select(y => new TileTemplate(this, y)).ToDictionary(t => t.Id);
 		}
 
-		public TileSet(string name, string id, string palette, string[] extensions)
+		public TileSet(string name, string id, string palette, string[] extensions, TerrainTypeInfo[] terrainInfo)
 		{
 			this.Name = name;
 			this.Id = id;
 			this.Palette = palette;
 			this.Extensions = extensions;
+			this.terrainInfo = terrainInfo;
+
+			for (var i = 0; i < terrainInfo.Length; i++)
+			{
+				var tt = terrainInfo[i].Type;
+
+				if (terrainIndexByType.ContainsKey(tt))
+					throw new InvalidDataException("Duplicate terrain type '{0}'.".F(tt));
+
+				terrainIndexByType.Add(tt, i);
+			}
+			defaultWalkableTerrainIndex = GetTerrainIndex("Clear");
+		}
+
+		public TerrainTypeInfo this[int index]
+		{
+			get { return terrainInfo[index]; }
+		}
+
+		public int TerrainsCount
+		{
+			get { return terrainInfo.Length; }
+		}
+
+		public bool TryGetTerrainIndex(string type, out int index)
+		{
+			return terrainIndexByType.TryGetValue(type, out index);
+		}
+
+		public int GetTerrainIndex(string type)
+		{
+			int index;
+			if (terrainIndexByType.TryGetValue(type, out index))
+				return index;
+
+			throw new InvalidDataException("Tileset '{0}' lacks terrain type '{1}'".F(Id, type));
+		}
+
+		public int GetTerrainIndex(TileReference<ushort, byte> r)
+		{
+			var tpl = Templates[r.Type];
+
+			if (tpl.Contains(r.Index))
+			{
+				var ti = tpl[r.Index];
+				if (ti != -1)
+					return ti;
+			}
+
+			return defaultWalkableTerrainIndex;
 		}
 
 		public void Save(string filepath)
@@ -138,21 +257,16 @@ namespace OpenRA
 			root.Add(new MiniYamlNode("General", null, gen));
 
 			root.Add(new MiniYamlNode("Terrain", null,
-				Terrain.Select(t => new MiniYamlNode("TerrainType@{0}".F(t.Value.Type), t.Value.Save())).ToList()));
+				terrainInfo.Select(t => new MiniYamlNode("TerrainType@{0}".F(t.Type), t.Save())).ToList()));
 
 			root.Add(new MiniYamlNode("Templates", null,
-				Templates.Select(t => new MiniYamlNode("Template@{0}".F(t.Value.Id), t.Value.Save())).ToList()));
+				Templates.Select(t => new MiniYamlNode("Template@{0}".F(t.Value.Id), t.Value.Save(this))).ToList()));
 			root.WriteToFile(filepath);
 		}
 
-		public string GetTerrainType(TileReference<ushort, byte> r)
+		public TerrainTypeInfo GetTerrainInfo(TileReference<ushort, byte> r)
 		{
-			var tt = Templates[r.Type].Tiles;
-			string ret;
-			if (!tt.TryGetValue(r.Index, out ret))
-				return "Clear"; // Default walkable
-
-			return ret;
+			return terrainInfo[GetTerrainIndex(r)];
 		}
 	}
 }
diff --git a/OpenRA.Game/Traits/World/ResourceLayer.cs b/OpenRA.Game/Traits/World/ResourceLayer.cs
index 1d024de7f8..e9f60a31bb 100644
--- a/OpenRA.Game/Traits/World/ResourceLayer.cs
+++ b/OpenRA.Game/Traits/World/ResourceLayer.cs
@@ -156,7 +156,7 @@ namespace OpenRA.Traits
 
 		CellContents CreateResourceCell(ResourceType t, CPos p)
 		{
-			world.Map.CustomTerrain[p.X, p.Y] = t.Info.TerrainType;
+			world.Map.CustomTerrain[p.X, p.Y] = world.TileSet.GetTerrainIndex(t.Info.TerrainType);
 			return new CellContents
 			{
 				Type = t,
@@ -194,7 +194,7 @@ namespace OpenRA.Traits
 			if (--content[p.X, p.Y].Density < 0)
 			{
 				content[p.X, p.Y] = EmptyCell;
-				world.Map.CustomTerrain[p.X, p.Y] = null;
+				world.Map.CustomTerrain[p.X, p.Y] = -1;
 			}
 
 			if (!dirty.Contains(p))
@@ -211,7 +211,7 @@ namespace OpenRA.Traits
 
 			// Clear cell
 			content[p.X, p.Y] = EmptyCell;
-			world.Map.CustomTerrain[p.X, p.Y] = null;
+			world.Map.CustomTerrain[p.X, p.Y] = -1;
 
 			if (!dirty.Contains(p))
 				dirty.Add(p);
diff --git a/OpenRA.Game/WorldUtils.cs b/OpenRA.Game/WorldUtils.cs
index 8f0fbee3cb..968dd636dc 100644
--- a/OpenRA.Game/WorldUtils.cs
+++ b/OpenRA.Game/WorldUtils.cs
@@ -88,15 +88,15 @@ namespace OpenRA
 		public const int MaxRange = 50;
 		static List<CVec>[] TilesByDistance = InitTilesByDistance(MaxRange);
 
-		public static string GetTerrainType(this World world, CPos cell)
+		public static int GetTerrainIndex(this World world, CPos cell)
 		{
 			var custom = world.Map.CustomTerrain[cell.X, cell.Y];
-			return custom ?? world.TileSet.GetTerrainType(world.Map.MapTiles.Value[cell.X, cell.Y]);
+			return custom != -1 ? custom : world.TileSet.GetTerrainIndex(world.Map.MapTiles.Value[cell.X, cell.Y]);
 		}
 
 		public static TerrainTypeInfo GetTerrainInfo(this World world, CPos cell)
 		{
-			return world.TileSet.Terrain[world.GetTerrainType(cell)];
+			return world.TileSet[world.GetTerrainIndex(cell)];
 		}
 
 		public static CPos ClampToWorld(this World world, CPos xy)
diff --git a/OpenRA.Mods.D2k/DamagedWithoutFoundation.cs b/OpenRA.Mods.D2k/DamagedWithoutFoundation.cs
index a1b7e3c759..6cbf576513 100644
--- a/OpenRA.Mods.D2k/DamagedWithoutFoundation.cs
+++ b/OpenRA.Mods.D2k/DamagedWithoutFoundation.cs
@@ -49,7 +49,7 @@ namespace OpenRA.Mods.Cnc
 			foreach (var kv in self.OccupiesSpace.OccupiedCells())
 			{
 				totalTiles++;
-				if (info.SafeTerrain.Contains(self.World.GetTerrainType(kv.First)))
+				if (info.SafeTerrain.Contains(self.World.GetTerrainInfo(kv.First).Type))
 					safeTiles++;
 			}
 
diff --git a/OpenRA.Mods.RA/AI/HackyAI.cs b/OpenRA.Mods.RA/AI/HackyAI.cs
index a0a1f1f453..9e4a1a555c 100644
--- a/OpenRA.Mods.RA/AI/HackyAI.cs
+++ b/OpenRA.Mods.RA/AI/HackyAI.cs
@@ -102,7 +102,7 @@ namespace OpenRA.Mods.RA.AI
 		BuildingInfo rallypointTestBuilding;
 		internal readonly HackyAIInfo Info;
 
-		string[] resourceTypes;
+		HashSet<int> resourceTypeIndices;
 
 		RushFuzzy rushFuzzy = new RushFuzzy();
 
@@ -152,8 +152,10 @@ namespace OpenRA.Mods.RA.AI
 
 			random = new MersenneTwister((int)p.PlayerActor.ActorID);
 
-			resourceTypes = Map.Rules.Actors["world"].Traits.WithInterface<ResourceTypeInfo>()
-				.Select(t => t.TerrainType).ToArray();
+			resourceTypeIndices = new HashSet<int>(
+				Map.Rules.Actors["world"].Traits
+				.WithInterface<ResourceTypeInfo>()
+				.Select(t => world.TileSet.GetTerrainIndex(t.TerrainType)));
 		}
 
 		static int GetPowerProvidedBy(ActorInfo building)
@@ -364,7 +366,7 @@ namespace OpenRA.Mods.RA.AI
 
 				case BuildingType.Refinery:
 					var tilesPos = world.FindTilesInCircle(baseCenter, MaxBaseDistance)
-						.Where(a => resourceTypes.Contains(world.GetTerrainType(new CPos(a.X, a.Y))));
+						.Where(a => resourceTypeIndices.Contains(world.GetTerrainIndex(new CPos(a.X, a.Y))));
 					if (tilesPos.Any())
 					{
 						var pos = tilesPos.MinBy(a => (a.CenterPosition - baseCenter.CenterPosition).LengthSquared);
diff --git a/OpenRA.Mods.RA/Air/Aircraft.cs b/OpenRA.Mods.RA/Air/Aircraft.cs
index e819c219a7..b633bdb6f7 100755
--- a/OpenRA.Mods.RA/Air/Aircraft.cs
+++ b/OpenRA.Mods.RA/Air/Aircraft.cs
@@ -171,7 +171,7 @@ namespace OpenRA.Mods.RA.Air
 			if (self.World.ActorMap.AnyUnitsAt(cell))
 				return false;
 
-			var type = self.World.GetTerrainType(cell);
+			var type = self.World.GetTerrainInfo(cell).Type;
 			return info.LandableTerrainTypes.Contains(type);
 		}
 
diff --git a/OpenRA.Mods.RA/Bridge.cs b/OpenRA.Mods.RA/Bridge.cs
index 7d78e8e802..aa34689d44 100644
--- a/OpenRA.Mods.RA/Bridge.cs
+++ b/OpenRA.Mods.RA/Bridge.cs
@@ -94,11 +94,11 @@ namespace OpenRA.Mods.RA
 				self.World.Map.CustomTerrain[c.X, c.Y] = GetTerrainType(c);
 		}
 
-		string GetTerrainType(CPos cell)
+		int GetTerrainType(CPos cell)
 		{
 			var dx = cell - self.Location;
 			var index = dx.X + self.World.TileSet.Templates[template].Size.X * dx.Y;
-			return self.World.TileSet.GetTerrainType(new TileReference<ushort, byte>(template, (byte)index));
+			return self.World.TileSet.GetTerrainIndex(new TileReference<ushort, byte>(template, (byte)index));
 		}
 
 		public void LinkNeighbouringBridges(World world, BridgeLayer bridges)
diff --git a/OpenRA.Mods.RA/Buildings/Bib.cs b/OpenRA.Mods.RA/Buildings/Bib.cs
index 95fb2ab413..ec5aeec250 100755
--- a/OpenRA.Mods.RA/Buildings/Bib.cs
+++ b/OpenRA.Mods.RA/Buildings/Bib.cs
@@ -52,7 +52,7 @@ namespace OpenRA.Mods.RA.Buildings
 				var cellOffset = new CVec(i % width, i / width + bibOffset);
 
 				// Some mods may define terrain-specific bibs
-				var terrain = self.World.GetTerrainType(location + cellOffset);
+				var terrain = self.World.GetTerrainInfo(location + cellOffset).Type;
 				var testSequence = info.Sequence + "-" + terrain;
 				var sequence = anim.HasSequence(testSequence) ? testSequence : info.Sequence;
 				anim.PlayFetchIndex(sequence, () => index);
diff --git a/OpenRA.Mods.RA/Buildings/LaysTerrain.cs b/OpenRA.Mods.RA/Buildings/LaysTerrain.cs
index c7455458f9..3dbe0b51f6 100755
--- a/OpenRA.Mods.RA/Buildings/LaysTerrain.cs
+++ b/OpenRA.Mods.RA/Buildings/LaysTerrain.cs
@@ -54,34 +54,34 @@ namespace OpenRA.Mods.RA.Buildings
 				foreach (var c in FootprintUtils.Tiles(self))
 				{
 					// Only place on allowed terrain types
-					if (!info.TerrainTypes.Contains(self.World.GetTerrainType(c)))
+					if (!info.TerrainTypes.Contains(self.World.GetTerrainInfo(c).Type))
 						continue;
 
 					// Don't place under other buildings or custom terrain
-					if (bi.GetBuildingAt(c) != self || self.World.Map.CustomTerrain[c.X, c.Y] != null)
+					if (bi.GetBuildingAt(c) != self || self.World.Map.CustomTerrain[c.X, c.Y] != -1)
 						continue;
 
-					var index = template.Tiles.Keys.Random(Game.CosmeticRandom);
-					layer.AddTile(c, new TileReference<ushort, byte>(template.Id, index));
+					var index = Game.CosmeticRandom.Next(template.TilesCount);
+					layer.AddTile(c, new TileReference<ushort, byte>(template.Id, (byte)index));
 				}
 
 				return;
 			}
 
 			var origin = self.Location + info.Offset;
-			foreach (var i in template.Tiles.Keys)
+			for (var i = 0; i < template.TilesCount; i++)
 			{
 				var c = origin + new CVec(i % template.Size.X, i / template.Size.X);
 
 				// Only place on allowed terrain types
-				if (!info.TerrainTypes.Contains(self.World.GetTerrainType(c)))
+				if (!info.TerrainTypes.Contains(self.World.GetTerrainInfo(c).Type))
 					continue;
 
 				// Don't place under other buildings or custom terrain
-				if (bi.GetBuildingAt(c) != self || self.World.Map.CustomTerrain[c.X, c.Y] != null)
+				if (bi.GetBuildingAt(c) != self || self.World.Map.CustomTerrain[c.X, c.Y] != -1)
 					continue;
 
-				layer.AddTile(c, new TileReference<ushort, byte>(template.Id, i));
+				layer.AddTile(c, new TileReference<ushort, byte>(template.Id, (byte)i));
 			}
 		}
 	}
diff --git a/OpenRA.Mods.RA/Buildings/Util.cs b/OpenRA.Mods.RA/Buildings/Util.cs
index 9021765a23..34dc19d896 100644
--- a/OpenRA.Mods.RA/Buildings/Util.cs
+++ b/OpenRA.Mods.RA/Buildings/Util.cs
@@ -26,7 +26,7 @@ namespace OpenRA.Mods.RA.Buildings
 			if (world.WorldActor.Trait<BuildingInfluence>().GetBuildingAt(a) != null) return false;
 			if (world.ActorMap.GetUnitsAt(a).Any(b => b != toIgnore)) return false;
 
-			return world.Map.IsInMap(a) && bi.TerrainTypes.Contains(world.GetTerrainType(a));
+			return world.Map.IsInMap(a) && bi.TerrainTypes.Contains(world.GetTerrainInfo(a).Type);
 		}
 
 		public static bool CanPlaceBuilding(this World world, string name, BuildingInfo building, CPos topLeft, Actor toIgnore)
diff --git a/OpenRA.Mods.RA/Crate.cs b/OpenRA.Mods.RA/Crate.cs
index cbe0b8f7a4..dbb798ce48 100644
--- a/OpenRA.Mods.RA/Crate.cs
+++ b/OpenRA.Mods.RA/Crate.cs
@@ -93,7 +93,7 @@ namespace OpenRA.Mods.RA
 		{
 			if (!self.World.Map.IsInMap(cell.X, cell.Y)) return false;
 
-			var type = self.World.GetTerrainType(cell);
+			var type = self.World.GetTerrainInfo(cell).Type;
 			if (!info.TerrainTypes.Contains(type))
 				return false;
 
diff --git a/OpenRA.Mods.RA/CrateSpawner.cs b/OpenRA.Mods.RA/CrateSpawner.cs
index c658f20c04..6956863acd 100644
--- a/OpenRA.Mods.RA/CrateSpawner.cs
+++ b/OpenRA.Mods.RA/CrateSpawner.cs
@@ -117,7 +117,7 @@ namespace OpenRA.Mods.RA
 				var p = self.World.ChooseRandomCell(self.World.SharedRandom);
 
 				// Is this valid terrain?
-				var terrainType = self.World.GetTerrainType(p);
+				var terrainType = self.World.GetTerrainInfo(p).Type;
 				if (!(inWater ? info.ValidWater : info.ValidGround).Contains(terrainType))
 					continue;
 
diff --git a/OpenRA.Mods.RA/Effects/Missile.cs b/OpenRA.Mods.RA/Effects/Missile.cs
index 22f27442c3..994dd98cf0 100755
--- a/OpenRA.Mods.RA/Effects/Missile.cs
+++ b/OpenRA.Mods.RA/Effects/Missile.cs
@@ -162,7 +162,7 @@ namespace OpenRA.Mods.RA.Effects
 				|| (info.RangeLimit != 0 && ticks > info.RangeLimit) // Ran out of fuel
 				|| (!info.High && world.ActorMap.GetUnitsAt(cell)
 					.Any(a => a.HasTrait<IBlocksBullets>())) // Hit a wall
-				|| (!string.IsNullOrEmpty(info.BoundToTerrainType) && world.GetTerrainType(cell) != info.BoundToTerrainType); // Hit incompatible terrain
+				|| (!string.IsNullOrEmpty(info.BoundToTerrainType) && world.GetTerrainInfo(cell).Type != info.BoundToTerrainType); // Hit incompatible terrain
 
 			if (shouldExplode)
 				Explode(world);
diff --git a/OpenRA.Mods.RA/Husk.cs b/OpenRA.Mods.RA/Husk.cs
index ef7065128b..3d2144ed03 100644
--- a/OpenRA.Mods.RA/Husk.cs
+++ b/OpenRA.Mods.RA/Husk.cs
@@ -58,7 +58,7 @@ namespace OpenRA.Mods.RA
 			if (!self.World.Map.IsInMap(cell.X, cell.Y))
 				return false;
 
-			if (!info.AllowedTerrain.Contains(self.World.GetTerrainType(cell)))
+			if (!info.AllowedTerrain.Contains(self.World.GetTerrainInfo(cell).Type))
 				return false;
 
 			if (!checkTransientActors)
diff --git a/OpenRA.Mods.RA/Move/Mobile.cs b/OpenRA.Mods.RA/Move/Mobile.cs
index 62d14b1017..f6b4117381 100755
--- a/OpenRA.Mods.RA/Move/Mobile.cs
+++ b/OpenRA.Mods.RA/Move/Mobile.cs
@@ -48,16 +48,55 @@ namespace OpenRA.Mods.RA.Move
 				var cost = nodesDict.ContainsKey("PathingCost")
 					? FieldLoader.GetValue<int>("cost", nodesDict["PathingCost"].Value)
 					: (int)(10000 / speed);
-				ret.Add(t.Key, new TerrainInfo { Speed = speed, Cost = cost });
+				ret.Add(t.Key, new TerrainInfo(speed, cost));
 			}
 
 			return ret;
 		}
 
+		TerrainInfo[] LoadTilesetSpeeds(TileSet tileSet)
+		{
+			var info = new TerrainInfo[tileSet.TerrainsCount];
+			for (var i = 0; i < info.Length; i++)
+				info[i] = TerrainInfo.Impassable;
+
+			foreach (var kvp in TerrainSpeeds)
+			{
+				int index;
+				if (tileSet.TryGetTerrainIndex(kvp.Key, out index))
+					info[index] = kvp.Value;
+			}
+
+			return info;
+		}
+
 		public class TerrainInfo
 		{
-			public int Cost = int.MaxValue;
-			public decimal Speed = 0;
+			public static readonly TerrainInfo Impassable = new TerrainInfo();
+
+			public readonly int Cost;
+			public readonly decimal Speed;
+
+			public TerrainInfo()
+			{
+				Cost = int.MaxValue;
+				Speed = 0;
+			}
+
+			public TerrainInfo(decimal speed, int cost)
+			{
+				Speed = speed;
+				Cost = cost;
+			}
+		}
+
+		public readonly Cache<TileSet, TerrainInfo[]> TilesetTerrainInfo;
+		public readonly Cache<TileSet, int> TilesetMovementClass;
+
+		public MobileInfo()
+		{
+			TilesetTerrainInfo = new Cache<TileSet, TerrainInfo[]>(LoadTilesetSpeeds);
+			TilesetMovementClass = new Cache<TileSet, int>(CalculateTilesetMovementClass);
 		}
 
 		public int MovementCostForCell(World world, CPos cell)
@@ -65,20 +104,22 @@ namespace OpenRA.Mods.RA.Move
 			if (!world.Map.IsInMap(cell.X, cell.Y))
 				return int.MaxValue;
 
-			var type = world.GetTerrainType(cell);
-			if (!TerrainSpeeds.ContainsKey(type))
+			var index = world.GetTerrainIndex(cell);
+			if (index == -1)
 				return int.MaxValue;
 
-			return TerrainSpeeds[type].Cost;
+			return TilesetTerrainInfo[world.TileSet][index].Cost;
+		}
+
+		public int CalculateTilesetMovementClass(TileSet tileset)
+		{
+			/* collect our ability to cross *all* terraintypes, in a bitvector */
+			return TilesetTerrainInfo[tileset].Select(ti => ti.Cost < int.MaxValue).ToBits();
 		}
 
 		public int GetMovementClass(TileSet tileset)
 		{
-			/* collect our ability to cross *all* terraintypes, in a bitvector */
-			var passability = tileset.Terrain.OrderBy(t => t.Key)
-				.Select(t => TerrainSpeeds.ContainsKey(t.Key) && TerrainSpeeds[t.Key].Cost < int.MaxValue);
-
-			return passability.ToBits();
+			return TilesetMovementClass[tileset];
 		}
 
 		public static readonly Dictionary<SubCell, WVec> SubCellOffsets = new Dictionary<SubCell, WVec>()
@@ -440,12 +481,15 @@ namespace OpenRA.Mods.RA.Move
 
 		public int MovementSpeedForCell(Actor self, CPos cell)
 		{
-			var type = self.World.GetTerrainType(cell);
-
-			if (!Info.TerrainSpeeds.ContainsKey(type))
+			var index = self.World.GetTerrainIndex(cell);
+			if (index == -1)
 				return 0;
 
-			decimal speed = Info.Speed * Info.TerrainSpeeds[type].Speed;
+			var speed = Info.TilesetTerrainInfo[self.World.TileSet][index].Speed;
+			if (speed == decimal.Zero)
+				return 0;
+
+			speed *= Info.Speed;
 			foreach (var t in self.TraitsImplementing<ISpeedModifier>())
 				speed *= t.GetSpeedModifier();
 			return (int)(speed / 100);
diff --git a/OpenRA.Mods.RA/RadarColorFromTerrain.cs b/OpenRA.Mods.RA/RadarColorFromTerrain.cs
index 930ec77f94..2c3033ab4d 100644
--- a/OpenRA.Mods.RA/RadarColorFromTerrain.cs
+++ b/OpenRA.Mods.RA/RadarColorFromTerrain.cs
@@ -25,7 +25,7 @@ namespace OpenRA.Mods.RA
 
 		public RadarColorFromTerrain(Actor self, string terrain)
 		{
-			c = self.World.TileSet.Terrain[terrain].Color;
+			c = self.World.TileSet[self.World.TileSet.GetTerrainIndex(terrain)].Color;
 		}
 
 		public bool VisibleOnRadar(Actor self) { return true; }
diff --git a/OpenRA.Mods.RA/Render/RenderLandingCraft.cs b/OpenRA.Mods.RA/Render/RenderLandingCraft.cs
index 37c6b26d2a..eb210b6c44 100644
--- a/OpenRA.Mods.RA/Render/RenderLandingCraft.cs
+++ b/OpenRA.Mods.RA/Render/RenderLandingCraft.cs
@@ -46,7 +46,7 @@ namespace OpenRA.Mods.RA.Render
 				return false;
 
 			return cargo.CurrentAdjacentCells
-				.Any(c => self.World.Map.IsInMap(c) && info.OpenTerrainTypes.Contains(self.World.GetTerrainType(c)));
+				.Any(c => self.World.Map.IsInMap(c) && info.OpenTerrainTypes.Contains(self.World.GetTerrainInfo(c).Type));
 		}
 
 		void Open()
diff --git a/OpenRA.Mods.RA/SupportPowers/ChronoshiftPower.cs b/OpenRA.Mods.RA/SupportPowers/ChronoshiftPower.cs
index 1221d8e1cf..92cf55cba5 100644
--- a/OpenRA.Mods.RA/SupportPowers/ChronoshiftPower.cs
+++ b/OpenRA.Mods.RA/SupportPowers/ChronoshiftPower.cs
@@ -71,36 +71,18 @@ namespace OpenRA.Mods.RA
 			var range = ((ChronoshiftPowerInfo)Info).Range;
 			var sourceTiles = self.World.FindTilesInCircle(xy, range);
 			var destTiles = self.World.FindTilesInCircle(sourceLocation, range);
-			var sourceTerrain = new List<string>();
-			var destTerrain = new List<string>();
 
-			int j = 0;
-			foreach (var t in sourceTiles)
+			using (var se = sourceTiles.GetEnumerator())
+			using (var de = destTiles.GetEnumerator())
+			while (se.MoveNext() && de.MoveNext())
 			{
-				j = j + 1;
-				if (!self.Owner.Shroud.IsExplored(t))
-					return false;
-				sourceTerrain.Add(self.World.GetTerrainType(t));
-			}
+				var a = se.Current;
+				var b = de.Current;
 
-			j = 0;
-			foreach (var t in destTiles)
-			{
-				j = j + 1;
-				if (!self.Owner.Shroud.IsExplored(t))
+				if (!self.Owner.Shroud.IsExplored(a) || !self.Owner.Shroud.IsExplored(b))
 					return false;
 
-				self.World.GetTerrainType(t);
-				destTerrain.Add(self.World.GetTerrainType(t));
-			}
-
-			// HACK but I don't want to write a comparison function
-			if (sourceTerrain.Count != destTerrain.Count)
-				return false;
-
-			for (int i = 0; i < sourceTerrain.Count; i++)
-			{
-				if (!sourceTerrain[i].Equals(destTerrain[i]))
+				if (self.World.GetTerrainIndex(a) != self.World.GetTerrainIndex(b))
 					return false;
 			}
 
diff --git a/OpenRA.Mods.RA/World/BuildableTerrainLayer.cs b/OpenRA.Mods.RA/World/BuildableTerrainLayer.cs
index b8be9a45d4..a452102d8e 100644
--- a/OpenRA.Mods.RA/World/BuildableTerrainLayer.cs
+++ b/OpenRA.Mods.RA/World/BuildableTerrainLayer.cs
@@ -38,7 +38,7 @@ namespace OpenRA.Mods.RA
 
 		public void AddTile(CPos cell, TileReference<ushort, byte> tile)
 		{
-			map.CustomTerrain[cell.X, cell.Y] = tileset.GetTerrainType(tile);
+			map.CustomTerrain[cell.X, cell.Y] = tileset.GetTerrainIndex(tile);
 
 			// Terrain tiles define their origin at the topleft
 			var s = theater.TileSprite(tile);
diff --git a/OpenRA.Mods.RA/World/DomainIndex.cs b/OpenRA.Mods.RA/World/DomainIndex.cs
index 6ca131fe07..994505913b 100644
--- a/OpenRA.Mods.RA/World/DomainIndex.cs
+++ b/OpenRA.Mods.RA/World/DomainIndex.cs
@@ -59,10 +59,6 @@ namespace OpenRA.Mods.RA
 		int[,] domains;
 		Dictionary<int, HashSet<int>> transientConnections;
 
-		// Each terrain has an offset corresponding to its location in a
-		// movement class bitmask.  This caches each offset.
-		Dictionary<string, int> terrainOffsets;
-
 		public MovementClassDomainIndex(World world, uint movementClass)
 		{
 			bounds = world.Map.Bounds;
@@ -70,14 +66,6 @@ namespace OpenRA.Mods.RA
 			domains = new int[(bounds.Width + bounds.X), (bounds.Height + bounds.Y)];
 			transientConnections = new Dictionary<int, HashSet<int>>();
 
-			terrainOffsets = new Dictionary<string, int>();
-			var terrains = world.TileSet.Terrain.OrderBy(t => t.Key).ToList();
-			foreach (var terrain in terrains)
-			{
-				var terrainOffset = terrains.FindIndex(x => x.Key == terrain.Key);
-				terrainOffsets[terrain.Key] = terrainOffset;
-			}
-
 			BuildDomains(world);
 		}
 
@@ -181,8 +169,7 @@ namespace OpenRA.Mods.RA
 
 		bool CanTraverseTile(World world, CPos p)
 		{
-			var currentTileType = WorldUtils.GetTerrainType(world, p);
-			var terrainOffset = terrainOffsets[currentTileType];
+			var terrainOffset = world.GetTerrainIndex(p);
 			return (movementClass & (1 << terrainOffset)) > 0;
 		}
 
diff --git a/OpenRA.TilesetBuilder/FormBuilder.cs b/OpenRA.TilesetBuilder/FormBuilder.cs
index a58f30d7f0..299c04b02f 100644
--- a/OpenRA.TilesetBuilder/FormBuilder.cs
+++ b/OpenRA.TilesetBuilder/FormBuilder.cs
@@ -367,7 +367,8 @@ namespace OpenRA.TilesetBuilder
 				name: tilesetName,
 				id: tilesetID.ToUpper(),
 				palette: tilesetPalette.ToLower(),
-				extensions: new string[] { ext[0], ext[1] }
+				extensions: new string[] { ext[0], ext[1] },
+				terrainInfo: TerrainType
 			);
 
 			// List of files to add to the mix file
@@ -381,30 +382,25 @@ namespace OpenRA.TilesetBuilder
 			foreach (var t in surface1.Templates)
 				fileList.Add(ExportTemplate(t, surface1.Templates.IndexOf(t), tileset.Extensions.First(), dir));
 
-			// Add the terraintypes
-			foreach (var tt in TerrainType)
-			{
-				tileset.Terrain.Add(tt.Type, tt);
-			}
-
 			// Add the templates
 			ushort cur = 0;
 			foreach (var tp in surface1.Templates)
 			{
+				var tiles = new int[tp.Width * tp.Height];
+				foreach (var t in tp.Cells)
+				{
+					string ttype = TerrainType[surface1.TerrainTypes[t.Key.X, t.Key.Y]].Type;
+					var idx = (t.Key.X - tp.Left) + tp.Width * (t.Key.Y - tp.Top);
+					tiles[idx] = tileset.GetTerrainIndex(ttype);
+				}
+
 				var template = new TileTemplate(
 					id: cur,
 					image: "{0}{1:00}".F(txtTilesetName.Text, cur),
-					size: new int2(tp.Width, tp.Height)
+					size: new int2(tp.Width, tp.Height),
+					tiles: tiles
 				);
 
-				foreach (var t in tp.Cells)
-				{
-					string ttype = "Clear";
-					ttype = TerrainType[surface1.TerrainTypes[t.Key.X, t.Key.Y]].Type;
-					var idx = (t.Key.X - tp.Left) + tp.Width * (t.Key.Y - tp.Top);
-					template.Tiles.Add((byte)idx, ttype);
-				}
-
 				tileset.Templates.Add(cur, template);
 				cur++;
 			}