Land Nav Task 12 - Locate an Unknown Point on a Map and on the Ground by Intersection

1.  
Use the map and compass method
(figure C-35).

Figure C-35.
Location of an unknown point

Note. The example map is not to scale-an easterly G-M angle
to 10 degrees is used in the examples.

a.
Determine the G-M angle of the
map you are using.

b.
Locate and mark your position
on the map.

c. 
Convert the magnetic azimuth to
the unknown point (22 degrees); change
it to a grid azimuth. In the example,
the G-M angle used was 10 degrees
easterly, giving a grid azimuth of 32
degrees.

d.
Place the protractor on the
map, ensuring that the zero-degree
indication on the protractor is
pointing to the top of the map (north)
and the index point is placed center
of mass on your location (figure
C-36). Place a tick mark at the number
of degrees you want to plot. Draw a
line on the map from your position on
this grid azimuth (32 degrees).

e.
Move to or call a second known
position from which the unknown point
can be seen. Locate this position on
the map.

f.  
Repeat steps 1c and 1d.

g.
Where the lines cross is the
location of the unknown point.

2.  
Use the straightedge method
(when no compass is available) (figure
C-36).

Figure C-36.
Intersection without compass

a.
See task number, 071-329-1012,
Orient a Map to the Ground by Map
Terrain Association.

b.
Locate and mark your position
on the map.

c. 
Lay a straightedge on the map
with one end at user’s position (A) as
a pivot point, and rotate the
straightedge until the unknown point
is sighted along the edge.

d.
Draw a line along the
straightedge.

e.
Repeat steps 2b, 2c, and 2d at
position (B) and, to check for
accuracy, at a third position.

f.  
The intersection of the lines
is the location of the unknown point
(C).