Ah, TPTB and their continuity errors, you think they would have learned from the '3 shot zat' by now. If it takes 3 ZPM's for the CIty to fully function, then the place must be as massive as the Manhattan scale shown above. But remember, if it takes at least 1 to power the shield, 1 to fully power the weapons, then logically it takes another one to operate the stardrive. And seeing you need the shield to protect the city from the vacuum of space, then I suppose it's theoretically possible to fly the city on just 2. But
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