Footprint
Circle of Visibility 
Mutual Visibility
A circular area on the ground, centered under the satellite.  Points
inside the circle have the satellite above their local horizon.  The footprint
does not look like a circle on the map when the satellite is near the poles,
due to the distorted map projection.  Footprints may be displayed by selecting
"Show Footprints" in the 
Main:Setup
menu.  Any two ground stations inside the footprint have a mutual visibility
window and can communicate via the satellite.
WinOrbit can display mutual visibility information in three ways: On the
Map (as described above); in the Report Window (via the 
Show DX
in the Map Window -   every station listed in the report has mutual visibility
with all the others at the time the report is generated); and in 
ephemeris printouts
(complete mutual visibility window listing from the observer to selected DX
sites over a period of time).  The latter report requires setting up the 
SPECIAL.QTH file.