There are many cities with single world-class scenes - Montreal for Deep learning, Honolulu for Surfing, etc. We could call these Scene cities. But it’s the convergence and intersection of scenes that makes for a Florence. The feeling of a Florence is one where Leonardo Da Vinci rubs shoulders with Machiavelli. Where Howard Hughes rubs shoulder with Humphrey Bogart.
This is a useful criteria because it suggests two things: