The idea is straightforward: spend a day travelling around your city / town / neighborhood and draw as much as possible all day long. Sketch 'till you crawl.
Over at sketchcrawl.com they have announced the second worldwide sketchcrawl on Sunday, March 6th.
If Pittsburgh's weather cooperates (meaning: not actually pouring with freezing rain and sleet) I think it sounds like a splendid project. I will figure out a place to start and confer with family on logistics and post more about this closer to that Sunday.