I started work on something pretty much like this about 5 years ago but never pursued it for various reasons.

I still have one of the registered domains with nothing to show for my preliminary work: www.tinynav.co.uk

I got as far as designing the encoding scheme, including a database of point types (house, utility pole, ancient monument, park, private event etc..), together with special codes for corporates to use for all their shops, fast food outlets etc.

I had the database tables worked out, populated the locations table with open source/public domain data such as civil and commercial airports and some other stuff. There was a front end that allowed for time-limited one-offs for things like 'Jo's birthday party', but then life took over!