Yes, the word 'Moscow' is a noun, a proper noun, the name of a specific place.
"Park Avenue" is a proper noun, because it is a place. Proper nouns like this should always be capitalized.
proper
No. Moscow is the fifth most populous city in the world, by city proper. It is, however, the largest city in Europe.
Common
common and proper
common
It is a proper noun, because it is the name of a specific thing.
common
it's a common noun. a proper noun would be Spider-Man.
As part of the city political limits or proper, yes. But the greater metropolitan area of Mexico City is much bigger:Population (city proper, 2015):Moscow: 12.2 millionMexico City: 8.9 millionPopulation (greater metropolitan area, 2015):Moscow: 16.8 millionMexico City: 21.2 million
Pencil proper or common noun