And here's some information on the important parts about maps. This confirms what I mentioned earlier, that Navteq supplies the data and each vendor then uses that data in their own proprietary formats. What this page doesn't have is any information on what Honda (specifically) is using. Honda is mentioned only historically.

Unfortunately the bin dumping and modifying information Bitt posted seems only useful to modify text and background images of the system, not actually modifying or taking apart the maps.