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Map Overlays (Range Rings; Lat/Long Grid)
The map screen can be customized with four range rings and/or grids
that divide the plotter into equal segments of latitude and longitude.
Range rings are handy for visually estimating distances on the map.
The ring diameters are based on the current zoom range. For example:
at the 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 to the third ring is 75 miles and
distance to the fourth ring is 100 miles from your current position.
To set range rings: From the Map Page, press
MENU|↓ to MAP
DATA|ENT. Press ↓ and → to RANGE RINGS. With the option highlighted,
press
ENT to check it (turn on) and uncheck it (turn off.) After the
option is set, press
EXIT|EXIT to return to the page display.
To set Lat/Long Grid: From the Map Page, press
MENU|↓ to MAP
DATA|ENT. Press ↓ and → to LAT/LON GRID LINES. With the option
highlighted, press
ENT to check it (turn on) and uncheck it (turn off.)
After the option is set, press
EXIT|EXIT to return to the page display.
Map Datum Selection
Maps and charts are based on a survey of the area that's covered by the
map or chart. These surveys are called "Datums." Maps that are
created using different datums will show the same latitude/longitude in
slightly different locations.
All datums are named. The GPS system is based on the WGS-84
datum, which covers the entire world. Other datums may also cover the
entire world, or just a small portion of it. By default, your unit uses the
WGS-84 datum. It, however, can show your position using one of 191
different datums. To change the datum:
1. Press
MENU|MENU|↓ to GPS SETUP|ENT|↓ to DATUM SELECTION|ENT.
2. Scroll ↓ or ↑ to select the desired datum, then press ENT.
3.
To return to the last page displayed, press EXIT|EXIT.
A list of the datums used by this unit is in the back of this manual.