asphalt jungle

(idiomatic) A city or urban area, where the landscape is covered by pavement and the environment is alienating and unsafe.

Example: 1962, "Manhattan's Lower Depths (film review of Strangers in the City)," Time, 27 Jul.,
  The sound track tingles with cool jazz, the dry atonal music of the asphalt jungle.
1976, A. Robert Lee, "Violence Real and Imagined: The World of Chester Himes' Novels," Negro American Literature Forum, vol. 10, no. 1, p. 13,
  Harlem comes through as an urban hothouse mean with exotic hustle and violence, a tangible asphalt jungle with its own abrasive laws of motion.