Garmin GDL 30A - Manual (Page 16)

 GDL 30A Owner’s Manual
Visibility
Visibility is the maximum horizontal distance that can be seen. Isobars on the Visibility feature show a change in visibility. Distance can be
displayed in nautical miles (nm), miles (mi.), or kilometers (km). See the chartplotter’s Owner’s Manual for more information on configuring
units of measure. In the example below, visibility ranges from 0.5 nautical miles to 3 nautical miles.
This image shows NEXRAD, Cloud Tops, and Visibility.
Displaying multiple features may help to provide a clearer
picture of the weather conditions in the area.
XM WX Weather Features