On a chart, how can I find the frequency for flight following? Is there a map I can refer to in order to pick up the correct frequency for VFR flight following while enroute? I know I can request a frequency from ATC as I depart, but what if I want to fly around and do sight seeing, practice maneuver for my checkride etc. for a while, then pick up flight following for the remainder of the trip?
In the United States, you can consult the VFR Sectional Chart and look for the frequency box located near a terminal area. 



Otherwise you'll need to consult the Airport Facility Directory for the region your are flying to find a ARTCC (Center) frequency.