I'm intrigued by the methodology you used to get these images. What's the threshold for what counts as a city? It obviously varies significantly from country to country.
Whatever your methodology was, it would be cool if you could cite a source/describe your methods in the description or caveats.
It seems to be according to official terminology and definitions. That is why Quebec and Nova Scotia are missing in Canada (Quebec doesn't have cities and towns but villes which cover both categories, while Nova Scotia uses broader municipal definitions). On the other hand, the UK is quite sparse seeing as city status is not often awarded.
Whatever your methodology was, it would be cool if you could cite a source/describe your methods in the description or caveats.