Quote:Has it been definitivley said in modern continuity that Metropolis is the Biggest city in the DCUs geography or does this only happen by the time the Legions 31st century rolls round?
I don't recall any specific instances stating as such, but it is often treated as being a surrogate New York, so I would say that it is a pretty good guess that it is one of the biggest in DC's United States.
Depends how modern is modern. The only specific one I remember was back during Zero Hour when they introduced Alpha Centurion. He was kidnapped from Earth by aliens a few thousand years ago and when they returned him in the modern era he told them to drop him off at Earth's largest city which he assumed would still be Rome but in the 1990s it was Metropolis. Which would be quite a feat since even New York can't claim to be the largest in the real world, Tokyo for example is larger.