"Dot dar" (the moving red/green dots) shows the position of enemy aircraft above 500 feet AGL, and within 12.5 miles (current settings in the MA), of a working radar tower, and the position of ALL friendly aircraft. "Bar dar" (the stationary red/green squares) shows the number (NOT position) of enemy/friendly aircraft and ground vehicles within a map sector.
Dot dar can be disabled locally by destroying the radar tower at a field. Both dot dar and bar dar can be disabled globally by damage to a country's HQ building. Enemy dot disappear first, then friendly dots, enemy bars, and firendly bars last.
So, if you see an unidentified plane in the distance, and there is no green dot in his general location on dot dar -- it is an enemy plane.