The population density has reduced a lot over the past 70 years, it has almost halved in some arrondissement (it's still among the highest density in the world

The population density has reduced a lot over the past 70 years, it has almost halved in some arrondissement (it's still among the highest density in the world though). You can find quite a lot apartments that used to be two smaller ones that have been merged together, especially in the upper floors.