Phoenix trails, especially South Mountain trails, are poorly documented. It would seem to me that on a given weekend enough people with GPSRs could plot the entire mountain. Sponsorship should be easy to get, REI, trail clubs, AZGeocaching, etc; maybe get the Parks Department involved. Assign hikers specific trails, hike the trails with "tracking" on, mark the "mileposts" as waypoints, download the tracks and waypoints on several strategically located laptops, and publish the results. Sell t-shirts, a nominal registration fee, etc., to cover costs.