I was sitting around thinking of some solutions for the getting-usable-data for GPS purposes problem today. I seem to recall some discussion about how commercially available data (i.e. NavTech) would be way to expensive. Well, I went to their website. I said I had a Clarion navigational unit, and tried to order a "map update". Well, it came to $105 for CA and NV maps (the whole US is $250). Apparently, this data is in SDAL format - if you register as a developer, you can download the spec for free (which I also did). So, the only question I have is if these "map updates" contain the whole map data, or just a subset thereof. I would assume that they contain everything since (a) they are gigantic, (b) since areas are sold seperately, it looks like the system was designed to let users upgrade their coverage.

So, does anyone have any reason(s) that I may have missed that would make this seem like not a good solution?