I currently work for a company that builds and maintains a navigable map product for several car companies. I cannot tell you too many specifics (due to NDA), but I can give you a basic overview.
a) the GIS software that is powering automobile navigation systems.
Are there any published specs, or are they completely proprietary
Completely proprietary. The "spec" will depend entirely upon which company/provider you are working with at the time. You will not be building a similar system on your own in any reasonable amount of time. Even being within a company that provides such a product, I only work on the mapping side. All of the routing and Geocoding happens via an utterly close-sourced system that is held (understandably) close to the chest.
b) what is the format of the street/network datasets? I dont have such
a fancy contraption in my vehicle, so I can't investigate for myself.
In North America (and perhaps South, as well), there are only two large contenders: NAVTEQ and TomTom (formerly Tele Atlas). The format of the datasets vary based on the customer, but I know that ArcMap is the most common due to ESRI's having a lot of the GIS market by the short hairs. It is important to note that, once the product is compiled onto the disk, it will no longer operate as normal vector/raster data (in my experience), and has to be read specifically by the proprietary software present in the car's navigation system.
I will be candid and say that, often, a DVD update will be pushed on a customer without any real reasoning behind it besides "NEW = GOOD." If you are keeping your sister's best interest in mind, my best advice is to stay informed and ask questions.
- In terms of raw data, how much information on the disk is new?
- If you already have a disk, how much benefit can you be expected to enjoy from upgrading?
- Have there been any major changes to the road network in your area that would suggest that an updated map disk is necessary? What were they? Can you prove they are in the product?
It is important to stick it to the salesman (who is selling the disk), because they will in turn rage at their map provider (who made the disk) who will then ask their data provider (who made the map data) for hard evidence to ensure that important things are not being left out and that the product being released is actually worth your hard earned moolah.