Map Item Format

Since Beta 1.6 craftable maps were added. They are placed in the "data" directory within the world's save directory. Each map has its own file associated with its ID and one file that keeps track of the highest (= most recently created) ID. This is limited to the size of a short (65,536).^[1] When Notch was adding them the first time he did not use NBT.^[2]

The structure tells that there will probably be an additional feature of maps with different zoom and size. There is support for Nether, but it is obscured and therefore unreadable.

[edit] Data folder structure

Each map starts with map_, have one unique number and ends with .dat. The file idcounts.dat contains the latest id for current map.

[edit] map_<id>.dat Format

This file has an incremental number in it. The name for the map is in the name of the file, as the name is not in the file.

[edit] NBT Structure

The structure of the file is as follows:

• TAG_Compound("")
  • TAG_Compound("data")
    • TAG_Byte("scale"): How zoomed in the map is (it is in 2^scale blocks square per pixel, even for 0, where the map will be 1:1). Default 3, minimum 0 and maximum 4.
    • TAG_Byte("dimension"): 0 = Overworld, -1 = Nether, 1 = The End
    • TAG_Short("height"): Height of map. Default (and only possible value) 128
    • TAG_Short("width"): Width of map. Default (and only possible value) 128
    • TAG_Int("xCenter"): Center of map according to real world by X
    • TAG_Int("zCenter"): Center of map according to real world by Z
    • TAG_Byte_Array("colors"): Width * Height array of color values (16384 entries for a default 128x128 map). Color can be accessed via the following method: colorID = Colors[widthOffset + heightOffset * width], where (widthOffset==0, heightOffset==0) is left upper point.

When this structure is loaded, Colors array is transformed to standard dimension (if it's necessary) and then structure is saved with standard height and width.

[edit] idcounts.dat Format

This file keeps track of the latest map added. Despite containing NBT tags, it is not an NBT file due lack of GZIP compression.

[edit] NBT Structure

The structure of the file is as follows:

• TAG_Short("map"): Current map id

[edit] Color table

The color IDs are sectioned in groups of 4. Darker color for water is deeper while other blocks is blending with each other.

[edit] Material Colors

Blocks are colored according to their Material (in the program code). Each Material has a base color which is multiplied by 180, 220 or 255 to make the map color. Some Materials share the same color; this table shows IDs for the Material Colors (multiply by 4 to get a Map Color ID).

[edit] References

1. ↑ http://twitter.com/notch/status/62970142207913984
2. ↑ http://twitter.com/notch/status/65360048049754112