The game already looks awesome!
I get a bit lost and wasn't able to find the continent i live on (Europe).
Maybe a Training could be added where the continents and cities have names and it starts with simple missions to just deliver to the right continent and later to popular cities. It could also be a game mode to just have popular cities.
Maybe you can get some inspiration for the gameplay from people playing GeoGuessr on YouTube.
Keep up the good work and thanks for providing a linux version!