Another approach of building a technical working navigation system, could be to use WiFi hotspots around the cities. If we could create a database, which has lots of hotspots in the city with it's locations, it should be easy to calculate positions within these hotspots. Google is tracking wifi networks with their streetview cars. Having the same approach that google has, but having it open.

Having a smartphone app would be a very handy thing. The smartphone app could just log all wifi networks while running in the background. The user could then decide if he/she wants to upload the logs immediately or later.
Is it allowed to do so? Are there any laws, regarding "stealing" somebodies wifi network name and signal strength?

is pretty awesome and can be found here:

There is a PDF document from Google explaining Google WiFi / GPS / cell tower navigation approaches which can be found here: