Minecraft map item format
From Just Solve the File Format Problem
The Minecraft map item format is used in the Java Edition of the Minecraft game. This and other Minecraft formats are extensively documented in the Minecraft Gamepedia wiki.
It is used to represent maps, in files saved by map ID (map_*.dat). The latest map ID is stored in a file idcounts.dat.
The Minecraft NBT format is used, with gzip compression.
