Land Nav Task 8 - Measure Distance on a Map

1.  
Identify the scale of the map.
The map scale is the ratio (1:50,000)
of the distance on the map (1 inch)
compared to the distance on the ground
(usually 50,000 inches).

2.  
Convert a straight-line map
distance to miles, meters, or yards
using the map’s bar scale (figure
C-27).

Figure C-27.
Bar scales

a.
For map distances equal to or
less than one inch:

(1) 
Line up the straight edge of a
strip of paper with the beginning and
ending points on the map.

(2) 
Mark on the straight edge of
the paper the beginning and ending
points (figure C-28).

Figure C-28.
Measuring distance

(3) 
Match the marks on the paper
with the appropriate bar scale (figure
C-29).

Figure C-29.
Determining distance

(4) 
Determine the distance on the
scale that compares to the distance on
the paper.

b.
For map distances greater than
one inch:

(1) 
Line up the straight edge of a
strip of paper with the beginning and
ending points on the map.

(2) 
Mark the beginning and ending
points on the straight edge of the
paper (figure C-28).

(3) 
Place the starting point on the
paper under the zero on the bar scale.

(4) 
Measure off 4,000 meters and
place a new tick mark on the paper.

(5) 
Place the new tick mark under
the zero on the bar scale.

(6) 
Determine if the end point
falls within the bar scale.

(a)  
Record the value on the scale
of the end point if the end point fits
on the scale.

(b)  
Add 4,000 meters to the value
you derived in step 2b(6)(a). This is
the total difference.

(7) 
Determine if the end point does
not fall within the bar.

(a)  
Repeat steps 2b(4) and (5)
until the end point falls within the
bar.

(b)  
Add 4,000 meters to the value
you derived in step 2b(6)(a) for each
time you performed step 2b(4). This is
the total difference.

3.  
Convert a road map distance to
miles, meters, or yards using the
map’s bar scale (figure C-28). This is
the actual distance you have to travel
to reach the point whose straight line
distance you identified in step 2.

a.
Line up the straight edge of a
strip of paper with the beginning
point and the point at which the road
makes the first curve on the map.

b.
Mark on the straight edge of
the paper the beginning and curve
points (figure 27).

c. 
Repeat steps 3a and b (each
time using the point of the curve as
the next beginning point) until you
reach the end point.

d.
Use step 3 to determine the
road distance in miles, meters, or
yards as appropriate.

(1) 
If the total distance measured
on the paper is equal to or less than
1 inch, use steps 2a(3) and (4).

(2) 
If the total distance measured
on the paper is more than 1 inch, use
steps 2b(3) through (7).