The characteristics in the location section of the audience builder stand for the following:
Top three cities
These are the three biggest cities in any given country e.g. Germany: Berlin, Hamburg and Munich
These are any other cities in any given country excluding the top three cities
Tip: if you select "top three cities" and "other cities" together, you get "urban" i.e. all the cities in a given country
All locations that are not a city.