Map item format

Maps do not store their information in the item; instead, they save a map number in the minecraft:map_id component that corresponds to the map number (ID) of a saved file. Their information is placed in the "data" directory within the world's save directory.

In Java Edition each map has its own file associated with its ID, and there is one file that keeps track of the highest (most recently created) map ID.

In Bedrock Edition each map can create 6 files, 1 associated with its original ID, 4 extra files that represent different scales of the map (which are stored as the parentMapIds), and another 1 extra file if the map was locked with a glass pane.