Map Format

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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.

Biome Values

Name Value
Ocean 0
Plains 1
Desert 2
Extreme Hills 3
Forest 4
Taiga 5
Swampland 6
River 7
Hell 8
Sky 9
Frozen Ocean 10
Frozen River 11
Ice Plains 12
Ice Mountains 13
Mushroom Island 14
Mushroom Island Shore 15
Beach 16
Desert Hills 17
Forest Hills 18
Taiga Hills 19
Extreme Hills Edge 20
Jungle 21
Jungle Hills 22


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


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)


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


Each region file is named "r.x.z.mca", where x and z are the coordinates. These coordinates are relative to each region. Given chunk column coordinates, divide them by 32 to get the region coordinates. Region files are not raw NBT files and must therefore be parsed differently see Region files. Every generated chunk has a 5-byte header with the first four bytes as the length of the compressed chunk in bytes and the fifth byte as the compression scheme.

Length of the compressed
chunk in bytes
Compression Scheme
Decoded 5033 zlib
On Disk(in hex) 00 13 A9 02

The compression scheme can have two value:

zlib 2
gzip 1

The notchian implementation will never compress with gzip but can read if provided.

Note: The following example is outdated. It is accurate for (at least) 1.4, but at some point the format has been changed. However, you will still need to support this version if you want reverse compatibility with old save files.

TAG_Compound(''): 2 entries
  TAG_Compound('Level'): 11 entries
    TAG_List('Entities'): List of entities in the chunk column
      TAG_Compound(): Each entity has a Tag_Compound
    TAG_List('Sections'): 5 entries
      TAG_Compound(''): 5 entries
        TAG_Byte('Y'): 0
        TAG_Byte_Array('BlockLight'): 2048 bytes
        TAG_Byte_Array('Blocks'): 4096 bytes
        TAG_Byte_Array('Data'): 2048 bytes
        TAG_Byte_Array('SkyLight'): 2048 bytes
      TAG_Compound(''): 5 entries
        TAG_Byte('Y'): 1
        TAG_Byte_Array('BlockLight'): 2048 bytes
        TAG_Byte_Array('Blocks'): 4096 bytes
        TAG_Byte_Array('Data'): 2048 bytes
        TAG_Byte_Array('SkyLight'): 2048 bytes
    TAG_Long('InhabitedTime'): 16
    TAG_Long('LastUpdate'): Last time a block changed in this column
    TAG_Byte('LightPopulated'): Is the light calculated
    TAG_Byte('TerrainPopulated'): Has the terrain been generated
    TAG_Int('xPos'): X position of the region. Each single increment to x is 512 blocks
    TAG_Int('zPos'): Z position of the region. Each single increment to z is 512 blocks
    TAG_Byte_Array('Biomes'): 256 bytes. Biomes affect blocks in 1x256x1 columns
    TAG_Int_Array('HeightMap'): 256 bytes
  TAG_Int('DataVersion'): 1343

See also

Region Files Tile entity format