[jokoon]

I always thought that a combination of a geohash-like z order curve over a 15km radius, with an offline gps coordinates list of the 5000 most populated cities on earth would be sufficient to cover 99% of people on earth.

Not sure what's the average number of characters required for a 20m to 100m precision with such method.

It's true that the idea of plus codes of using city names makes a lot of sense.

[mro_name]

I once heard a really unique orientation talk about http://www.volksnav.com – based on the idea of polar coordinates like on an imagined clock dial flat on earth centered at your local reference point (e.g. city center) and 12 o'clock = south. Used in one city in Brazil, I think.