Possible on screen positions.

ON_SCREEN_POSITION_UNSPECIFIED On screen position is not specified in this version. This enum is a place holder for a default value and does not represent a real on screen position.
ON_SCREEN_POSITION_UNKNOWN The ad position is unknown on the screen.
ON_SCREEN_POSITION_ABOVE_THE_FOLD The ad is located above the fold.
ON_SCREEN_POSITION_BELOW_THE_FOLD The ad is located below the fold.