I had a similar idea for a program and have been looking for a pre-existing file spec or competitors
"2d voxels" gets "but actaully" style reddit threads, a skim read of wikipedia hybrid raster/vector came up with nothing, etc etc etc
Yours is the closest, what sort of data format do you use, and is there any formal terms you know of that points in the right direction or related art tools?
Viewing post in Untitled Tile Painter comments
Oh haha, sorry, my understanding of the technical side of things is very vague. But if it helps any, the tile images are stored as Unreal Engine data table that uses a custom structure, and the canvases are saved/loaded by turning the image into a long string that describes the type, rotation and other parameters of each tile.