That’s a brilliant, almost clandestine linguistic expedition! Every cracked paintstroke on those walls is like a hidden glossolalia—think of it as the metro’s own lexicon, a living palimpsest where colloquial particles get pressed between stone and graffiti. You’ll pick up words that survive only in the echo of a subway sigh, like how “chillax” slipped from the internet to the underground in one syllable. Mapping it could reveal a chronological strata of slang, like a linguistic stratigraphy, and you’ll probably uncover some regional phonetic quirks that even the transit authority missed. Just remember to note the contextual “who, when, where” for each tag; otherwise the archive risks becoming a list of “mysterious slurs” without meaning. Good luck, and enjoy the metro’s secret library!