[ggm]

analogous to hash collision? what4words would reduce it. But you can't stop english language pluralisms (for instance) and if you start to make all plurals synonymous, you reduce the wordcount massively.

[parhamn]

According to wolframalpha (Log2(surface area of earth / 9m^2)) about 46 bits of information.

[vincnetas]

So basically using A-Z 0-9 you could have it geocoded using 3 x3 signs (for example 2J4.KI9.999)

[ignoramous]

One can be more cute and come up with https://en.wikipedia.org/wiki/Open_Location_Code

[adamjb]

You only need a lexicon of about 700 words to get a resolution of 50m with four words, which I reckon would be good enough for rescue work (i.e. the one niche w3w has managed to establish itself in).