Land Nav Task 8 - Measure Distance on a Map
Standards: 1. Determined the straight-line distance, in meters, between two points, with no more than five percent error. 2. Determined the road (curved line) distance, in meters, between two points, with no more than ten percent error.

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).

1.   Identified the scale of the map.

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2.   Converted the straight-line map distance to miles, meters or yards using the map's bar scale with no more than 5 percent error.

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3.   Converted the road map distance to miles, meters, or yards using the map's bar scale with no more than 10 percent error.

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References

Required

Related

FM 3-25.26