Officially the entire ghost population lives within the city area since it’s the only place in the world they’re legally allowed to! Leaving the city is permitted for a limited time (for work purposes); leaving the country is not. The government takes these measures to prevent the virus from spreading further

That said, a few adventurous types have attempted to sneak out into neighboring countries but it has never ended happily. If/when they get caught the punishment is harsh on either side of the border :’)