Is metropolis a proper on common noun?

"Metropolis" can be both a proper noun and a common noun, depending on how it's used:

Proper Noun:

* When referring to a specific city: "I visited the Metropolis of New York City." Here, "Metropolis" is referring to the actual city of New York, making it a proper noun.

* When referring to a specific fictional city: "Superman lives in the Metropolis of Metropolis." Here, "Metropolis" is referring to the specific fictional city from the Superman comics, making it a proper noun.

Common Noun:

* When referring to any large city in general: "A metropolis is usually a large city with a dense population and significant economic activity." Here, "metropolis" is referring to any large city, making it a common noun.

So, to know if "Metropolis" is a proper noun or a common noun, you need to look at how it's being used in a specific sentence.