There is also a bias in the rating range of a city. E.g. in Berlin when looking to go out to eat I'd look for 4.5 and above as it uses quite a wide range for ratings, while e.g. in Rome most time I'd be happy with a 4.0. There are many phenomena (in Rome probably high tourist expectations) that can skew the distribution of reviews in a way that makes it hard to use as a "quality" scale.