What you have described here is - near enough - close to what I know the Philips Carin nav system does (I worked on it at Philips in Eindhoven a number of years ago). There is a "parsing" mechanism to step through a detail hierarchy of the map supplied from the CD ROM.

Have you considered using the CARIN navigation disks as map sources for the project? These are freely available at CARIN dealers and you can subscribe to an update plan. The format and content is described in various techinical publications available directly from Philips on request. I am not sure what map coverage is like outside Europe; they are however a hierarchy database which allows the generation of vector based maps and are generated by the European Digital Mapping project which is a collaboration between various different national mapping concerns (such as OS in the UK).

One of the few remaining Mk1 owners... #00015