This file contains additional information, probably added from the digital camera or scanner used to create or digitize it.
If the file has been modified from its original state, some details may not fully reflect the modified file.
In this video you can see the basics of Design Your Own Mission. This is a GTA mod(ification) that allows you to create missions ingame, without any knowledge of scripting. The missions can also be distributed and played by others. You can download the mod at gtagarage.com, and you can find a lot of missions made by others at http://dyom.gtagames.nl.