When looking at streams, there are 3 broad descriptors of its physical condition:

• Is it open, and flowing in a largely non-engineered channel? (indicated in blue)
  
• Is it open, but channelized, which means the sides or bottom
  or both have been hardened with concrete or rip-rap or other means? (indicated in orange)
  
• Is it culverted?
  That is, is it now underground? (indicated in red)
  
  The map uses the best available data for the county, from 1992/93
  
  Note the blank spots in what is the urban center of Pittsburgh, where did all the streams go?