Minecraft wiki entry for Data_version, associated text:  r.x.z.mca: Information about the region at exact region coordinates [x,y] (1 region = 32×32 chunks)
 Chunk [x1,y1]   in world at (x2,y2): Information about the chunk at relative chunk coordinates [x1,y1], located at exact chunk coordinates [x2,y2] (1 chunk = 16×16 blocks)
 DataVersion: An integer displaying the data version.