Garmin G300 Pilot's Manual page 179

RUNWAyS
warning: Do not use Synthetic Vision runway depictions as the sole
means for determining the proximity of the aircraft to the runway or for
maintaining the proper approach path angle during landing.
nOte: Not all airports have runways with endpoint data in the database,
therefore, these runways are not displayed.
Runway data provides improved awareness of runway location with respect to
the surrounding terrain. All runway thresholds are depicted at their respective
elevations as defined in the database. In some situations, where threshold
elevations differ significantly, crossing runways may appear to be layered. As
runways are displayed, those within 45 degrees of the aircraft heading are
outlined in white. Other runways (those NOT aligned with the aircraft heading)
are outlined in gray. When an approach for a specific runway is active, that
runway appears brighter and is outlined with a white box, regardless of the
runway orientation as related to aircraft heading. As the aircraft gets closer to
the runway, more detail such as runway numbers and centerlines are displayed.
Runway
Selected for
Approach
190-00921-00 Rev. D
Airport Runways
Garmin G300 Pilot's Guide
additional Features
Other
Runway on
Airport
161