The red, purple, and blue lines correspond to the "local", "distant", and "fringe" coverage areas of each radio station:

• Local Coverage: Within this area, you should be able to receive the radio station on almost any radio with moderately good to very good reception.
  
• Distant Coverage: Within this area, the signal of the radio station may be weak unless you have a good car radio or a good stereo with a good antenna. You may not be able to receive the station at all on walkmans or other portable radios.
  
• Fringe Coverage: Within this area, the station's signal will be very weak. You may be able to receive this station if you have a very good radio with a good antenna, but it's possible that interference from other stations may prevent you from picking up these stations at all.