I'd say it is the other way around. Trying to quarantine a city / aim for zero cases only make sense because the larger area it's easy to shut itself out at the

I'd say it is the other way around. Trying to quarantine a city / aim for zero cases only make sense because the larger area it's easy to shut itself out at the country level. Lockdowns are not 100% effective, but just an attempt to slow down the transmission rate. Think of it as a type of defense-in-depth. Australia (and New Zealand's) true advantage is their natural isolation from the rest of the world and their ability to control/track who is coming into the country.