GM 100 manual doesn't explain use of MapFix.
The same feature is explained in downloadable GM1600 manual.
The following is a clip from this manual:
Map Fix is used with charts or maps. This system asks for a reference
position in latitude/longitude, which you take from a marked location on
the map. It then shows the present position as distance on the map from
that reference point. For example, if it shows a distance of UP 4.00Ē and
LEFT 0.50Ē, you then measure up four inches and to the left a half-inch
from the reference point on the map to find your location.
To use this format, you need to follow these steps in order. First, take
your map of the area and determine a reference latitude/longitude. (Note: in
order for this system to work, the latitude/longitude lines must be parallel
with the edge of the map. USGS maps are parallel, others may not be.
Also, this works better with smaller scale maps.) The reference position
can be anywhere on the map, but the closer it is to your location, the
smaller the numbers will be that youíll have to deal with.
Once youíve decided on a reference position, youíll need to save it as a
waypoint. See the waypoint section for information on saving a waypoint
using the EDIT Position method. Save the reference position as a waypoint.
Exit from the waypoint screens.
Press the MENU key, then select GPS Setup.
Highlight "MAP FIX SETUP" and press the right
arrow key. The screen at right appears. "REFERENCE
POINT" is highlighted. Press the right arrow
key. Select the waypoint number that you
saved the reference point under. Highlight the
"SET REFERENCE" label and press the right arrow
key. The unit returns to the Map Fix Setup
menu. Now highlight the Map Scale label and
press the right arrow key. Enter the mapís scale. This is generally at the
bottom of the paper map. Itís shown as a ratio, for example 1:24000. In
this example, we entered 24000 as a map scale. (Ignore the 1:) The unit
returns to the Map Fix Setup screen.
Finally, press the EXIT key to erase this menu. Now select "POSITION
FORMAT". Select Map Fix from the list and press the EXIT key. All position
information now shows as a distance from the reference point you
entered and saved as a waypoint earlier.
Copyright © 1996, 1997, 1998 Lowrance Electronics, Inc.