When to Capitalize "City": Proper Noun vs. Common Noun

The word "city" is capitalized only when part of a proper noun. Example: "I live in New York City." Here, "City" is part of the official name. As a common noun, it is lowercase: "I live in a city." The same rule applies to "state," "country," "river," etc.—capitalize only in proper names (e.g., New York State, but "the state of New York").