The 'gmap' folder contains numerous files and folders. Many of these files are graphical files explained how to edit in guides in the Graphic Editing folder. In the '3d' sub-folder are some new extensions I'm not too familiar with. I'm guessing '3d' is for 3D data. That being said the files in this folder are compressed with LZ77 (I think so, anyway) and for more detail feel free to research 3D graphics by googling it and looking up popular hacking sites with good resources such as http://www.gbatemp.net.