Map Format

This page covers the world information as of 1.2.5 to the present. See Alpha Map Format for Alpha information.

General Information
Worlds are represented as a series of regions, within which are a number of columns, and chunks. Each region is 32x1x32 columns, each column is 1x16x1 chunks, and each chunk is 16x16x16 blocks. The overall block height of a column is 256. Each chunk stores four (or five) things - block IDs (8-bit), block metadata (4-bit), block light (4-bit), and sky light (4-bit). The optional fifth value is "add" data, which is four bits to be added to block IDs for additional block ID support (not used in vanilla Minecraft). Block light is light cast by things like torches and glowstone, and is calculated with a 3D Flood Fill algorithm. Sky light is the light cast by the sky, and is calculated by starting at the top and working your way down. As you pass through semi-transparent blocks, you decrease the lighting value until you hit an opaque block. The opaque block is the last block whose skylight has a nonzero value. Lighting starts at 0xF (brightest) and works down to 0x0 (dimmest). Columns store biome information. Each 1x256x1 cuboid of blocks has the same biome value, for a total of 256 possible biome values per chunk (16x16). Biome values are stored as bytes.

Storage
This section documents the Anvil format for servers.

Maps are stored as a specific directory structure with several NBT files within. For the sake of examples, the world we'll be working with is stored in a folder called "/world".

Directory Structure

 * /world/data: Unused
 * /world/DIM-1: Nether world
 * /world/DIM-1/region: Nether world regions
 * /world/DIM1: End world
 * /world/DIM1/region: End world regions
 * /world/players: Player data
 * /world/region: Overworld regions

level.dat
In the root directory is a level.dat file. The structure of that file is this:


 * NBTCompound(Data)
 * NBTByte(hardcore)
 * NBTByte(MapFeatures): Set to 1 if structures are generated, such as villages
 * NBTByte(raining): Set to 1 if currently raining
 * NBTByte(thundering): Set to 1 if currently thundering (only if there is potential for thunder, not if a thunderbolt is currently in progress)
 * NBTInt(GameType)
 * NBTInt(generatorVersion): 0 for 1.2.5
 * NBTInt(rainTime): The ticks remaining until rain stops?
 * NBTInt(SpawnX)
 * NBTInt(SpawnY)
 * NBTInt(SpawnZ)
 * NBTInt(thunderTime)
 * NBTInt(version): 19133 for 1.2.5
 * NBTLong(LastPlayed)
 * NBTLong(RandomSeed)
 * NBTLong(SizeOnDisk): Always 0 for 1.2.5
 * NBTLong(Time)
 * NBTString(generatorName)
 * NBTString(LevelName)

[playeruuid].dat
Each player that has ever connected is given a [playeruuid].dat file.


 * NBTCompound
 * NBTByte(OnGround)
 * NBTByte(Sleeping)
 * NBTShort(Air)
 * NBTShort(AttackTime)
 * NBTShort(DeathTime)
 * NBTShort(Fire): Ticks until the player is no longer on fire, or zero
 * NBTShort(Health)
 * NBTShort(HurtTime)
 * NBTShort(SleepTimer)
 * NBTInt(Dimension)
 * NBTInt(foodLevel)
 * NBTInt(foodTickTimer)
 * NBTInt(playerGameType)
 * NBTInt(XpLevel)
 * NBTInt(XpTotal)
 * NBTFloat(FallDistance)
 * NBTFloat(foodExhastionLevel)
 * NBTFloat(foodSaturationLevel)
 * NBTFloat(XpP)
 * NBTCompound(Inventory)
 * NBTCompound
 * NBTByte(Count)
 * NBTByte(Slot)
 * NBTShort(Damage): Damage -or- metadata
 * NBTShort(id)
 * NBTList(Motion)
 * NBTDouble
 * NBTDouble
 * NBTDouble
 * NBTList(Pos)
 * NBTDouble
 * NBTDouble
 * NBTDouble
 * NBTList(Rotation)
 * NBTFloat
 * NBTFloat

[region].mca
Each region file is named "r.x.z.mca", where x and z are the coordinates. These coordinates are relative to each region. Given column coordinates, divide them by 32 to get the region coordinates.


 * NBTCompound
 * NBTCompound(Chunk [x,z]): x and z are region column coordinates, not relative to the overall world. The compound name is a misnomer, it actually represents column.
 * NBTCompound(Level)
 * NBTByte(TerrainPopulated): 1 if this column has been generated
 * NBTInt(xPos): In global, world-relative chunk coordinates
 * NBTInt(yPos): In global, world-relative chunk coordinates
 * NBTLong(LastUpdate): The last time a block changed in this column
 * NBTByteArray(Biomes)
 * NBTList(Entities)
 * NBTCompound
 * NBTByte(OnGround)
 * NBTShort(Air)
 * NBTShort(AttackTime)
 * NBTShort(DeathTime)
 * NBTShort(Fire)
 * NBTShort(Health)
 * NBTShort(HurtTime)
 * NBTFloat(FallDistance)
 * NBTString(id): Example: "Skeleton"
 * NBTList(Motion)
 * NBTDouble
 * NBTDouble
 * NBTDouble
 * NBTList(Pos)
 * NBTDouble
 * NBTDouble
 * NBTDouble
 * NBTList(Rotation)
 * NBTFloat
 * NBTFloat
 * NBTList(Sections): Chunks
 * NBTCompound
 * NBTByte(Y): 0-16
 * NBTByteArray(BlockLight)
 * NBTByteArray(Blocks)
 * NBTByteArray(Data)
 * NBTByteArray(SkyLight)
 * NBTList(TileEntities)
 * See this
 * NBTIntArray(HeightMap)