Much maligned on Hacker News though it is, this is precisely the killer application that what3words is good for.

It works offline on cheap android devices with GPS for discovery, which can also be done with a satellite map. Directions via an intent into another app with nav is now built into the main apps.

In fact, it's already used for doctors finding women in labour in improvised settlements in South Africa.

Disclosure: former employee, who wishes them all the luck in the world getting people to use it!