Many rappers and hip-hop icons often pay homage to their origins by referencing it as its area code. This was done for Chicago and LA to name a few. 313 is actually the area code for Detroit, Michigan, a place known for its rappers and “difficult” interior. The most famous rapper to use this slang is Eminem where he made a song titled “313” that references his hardship, skills, and experiences in Detroit. While you may not be Eminem, you can still use this slang like this:
“313 is a place I want to visit but not stay in. Life’s tough there.”
Nowadays, you would only hear this slang from rappers, urban people, and people from Detroit.