[Normille]

This new-fangled Google feature and the resulting Plus Codes actually reminds me quite a bit of Open Postcode [1] system which I read about many years ago but which, unfortunately, never seems to have progressed beyond a proof-of-concept, covering only Ireland. I actually think the Open Postcode system is a bit more flexible as you can increase/decrease the accuracy by varying the number of characters:

  >For geolocation applications: at eight characters it extends to an accuracy of an average radial offset of ~.58m (inside an area just 1.2m x .92m), while the code is easily extended with even further characters. At 9 characters it is down to centimetre scale. At 10 characters it can provide geolocation coding for the entire globe. 

With the weight of Google behind it, Plus Codes should get more traction than Open Postcode did. But, with the fickleness of Google behind it, is equally likely to be taken out the back and shot a couple of years down the line.

  >How is this different from What3words?

Because this actually make sense, whereas What3words is the stupidest idea of all time [1].

[0] http://www.openpostcode.org/

[1]https://stiobhart.net/2016-01-15-stupidest-idea-ever/