There are multiple issues with the What3Words algorithm.

For many squares in cities in the UK, there are a series of other squares which will only vary by one of the three words i.e. two of the words are common e.g. ///bank.fine.fishery and ///bank.fine.even. These relationship between these squares is predictable.

The distance between these squares that only vary by a word is often below 50km, but can be under 1km.

For some of these squares, the only variation in that remaining different word with be a single letter “s” e.g. ///bank.fine.fishery and ///bank.fines.fishery.

Certain word pairs – such as take/takes, fine/fines, plot/plots, bump/bumps and space/spaces – are more likely to result in close pairs.

This same issue can impact other errors such as spelling mistakes and homophones.

The word list is limited to 2,500 words in cities in the UK, greatly increasing the probability of these errors happening.

A side effect of defining these densely populated areas results in some of these pairs of squares being even closer than they would be normally.

Combining these issues means that there are many squares under 10km apart that can be confused by changing a word to and from a plural.