Pittsburgh was a large city located in Pennsylvania, United States of America, on the planet Earth.
Selma Guitierrez, a MACO with the Enterprise (NX-01) was raised in Pittsburgh after being born in Minnesota. (ENT novels: Last Full Measure, The Good That Men Do)
Benjamin Sisko, a baseball fan, owned and wore a baseball cap belonging to the Homestead Grays, a team in the city in the early to mid-20th century, on occasion. (DS9 episode: "Emissary")