On the FSDeveloper Wiki we have a page describing the FSX autogen (AGN) file format. Today I have been experimenting with AGN files a bit, so I have added more information to this page. Polygonal buidlings, library objects and row houses are not also described. For the other sections I have added some extra explanation as well.
Why did I do this? I wanted to see if I can create AGN files based on shapefile footprints of buidlings. So understanding the AGN format was the first step in that process. I have now made a small tool that can decompile a AGN file into a text file. My next step will be to make a compiler to do the reverse step. The last step would then be to make a small tool to turn the shapefile information into such a text file for my compiler.
I am not sure if compiling and decompiling AGN files is useful to other developers. If you think it might be useful let me know.