There doesn't appear to be any way to use NBT tags to create exploration maps of a given area, showing a structure using the Decorations tag. It would be nice, because the exploration maps look very good
Comments 4
It would still be nice if there were a way to set a certain flag in map##.dat or something that would automatically fill it in using the heightmap style the same way that it is when generated by a cartographer villager
Map data is not saved in the item, but instead in world/data/map##.day.
You can add the icons using the Decorations item tag though.