Metafiles vary so widely in format that it is pointless to attempt to construct a hierarchical explanation of their general construction. Most metafiles contain some sort of header, followed by one or more sections of image data. Some metafiles contain nothing but bitmap data, and still others contain no data at all, opting instead for cryptic drawing instructions, or numerical data similar to that found in vector files.
This page is taken from the Encyclopedia of Graphics File Formats and is licensed by O'Reilly under the Creative Common/Attribution license.