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Draw Map Boundaries
From the Map Data menu, press ↓ to
DRAW MAP BOUNDARIES. With the
option highlighted, press
ENT to turn it on (check) or turn it off (un-
check). After the option is set, press
EXIT.
Fill Water with White
From the Map Data menu, press ↓ to
FILL WATER WITH WHITE. With the
option highlighted, press
ENT to turn it on (check) or turn it off (un-
check). After the option is set, press
EXIT.
Map Overlays (Range Rings, Lat/Long Grid)
The map screen can be customized with range rings and/or grids that
divide the plotter into equal segments of latitude and longitude.
Range rings are handy for estimating distances on the map. Ring di-
ameters are based on the current zoom range. At a 100-mile zoom, the
screen will show two rings with your current position in the center. The
large ring touching the left and right sides of the screen is 100 miles in
diameter (same as the zoom range). The second, smaller ring is 50
miles in diameter (always 1/2 the zoom range).
The distance from your current position to the smaller ring (the ring's
radius) is 25 miles (always 1/4 the zoom range). With the arrow keys
and map cursor, you can scroll the map to see the third and fourth
rings. In this example, the distance from your current position to the
third ring is 75 miles and distance to the fourth ring is 100 miles.
To set range rings: From the Map Data menu, press ↓ to
RANGE RINGS.
With the option highlighted, press
ENT to turn it on (check) or turn it
off (uncheck).
To set Lat/Lon Grid Lines: From the Map Data menu, press ↓ to
LAT/LON GRID LINES. With the option highlighted, press ENT to turn it on
(check) or turn it off (uncheck). After the option is set, press
EXIT|EXIT
to return to the main page display.
Map Datum Selection
Maps and charts are based on a survey of the area covered by the map
or chart. These surveys are called Datums. Maps created using differ-
ent datums will show the same latitude/longitude in slightly different
locations.
The GPS system is based on the WGS-84 datum, which covers the en-
tire world. Other datums may also cover the entire world or just a
small portion of it. By default, your position is shown using the WGS-84
datum. It, however, can show your position using any of 191 different
datums.