LESSON 6
MAP READING
MEASURING DISTANCES ON MAPS
Reference:
Aids:
Manual of Map Reading and Land Navigation
1.
Slide 6/1 to 6/7.
Place of Work:
2.
1:50,000 map sheet per student.
Classroom
3.
Pencil, paper and ruler per student.
Student Dress:
Administration:
Working Dress
1.
Read the Instructors Notes before the
lesson.
Equipment:
2.
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3.
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4.
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5.
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Projector and Screen
Time Allowed:
40 Minutes
6-1
BEGINNING OF LESSON
STAGE
Revision
CONTENT
If two points are 4km apart on the ground, what is the distance between
the same two points on a 1:50,000 map?
ANSWER: 8cm
If two points are 6cm apart on the map, how far apart are the same two
points on the ground?
ANSWER: 3km
Where are the scale lines shown on M726 maps?
ANSWER: In the centre at the bottom of the map.
Aim
The aim of this lesson is to teach you how to estimate and measure
distances on maps.
Objectives
By the end of this lesson students will be able to:
1.
Estimate straight line distances on maps.
2.
Measure both straight line and indirect distances on maps using
the paper strip method.
3.
Use the map scale line.
Reasons Why
You need to be able to measure distances on maps to help work out
timings for troop movements.
Incentive
You do not want to move to a new location and miss an RV because
you have miscalculated the distance.
If you are siting support weapons you will want to be able to select
defensive fire locations, and work out their range before any action
takes place.
6-2
MIDDLE OF LESSON
STRAIGHT LINE
DISTANCE
This is the shortest distance between two place on the map or ground.
It is the “as the crow flies” distance. It can be easily measured on the
map, but takes no account of the rise and fall of the ground along the
line.
ESTIMATING
STRAIGHT LINE
DISTANCES
If a straight line distance is nearly North to South, or nearly East to
West it can be compared to the nearest grid lines. Each pair of grid
lines are two centimetres apart and represent one kilometre.
SLIDE 6/1
If the line to be measured is roughly diagonal to the grid, you can
estimate the distance because each diagonal is just under 1.5km.
(Confirm this before continuing).
Note: If you carefully measure 3 diagonal squares, it is not exactly
4.5km but a little less.
THE SERIES M726 The scale lines on Series M726 are known as party divided.
SCALE LINE
The first kilometre is divided into tenths of a kilometre and its righthand end is the zero mark. To the right of the zero are the main
kilometre divisions.
SLIDE 6/2
EXPLAIN that to measure a line to the nearest tenth of a kilometre,
the right-hand end of the line should be set on a whole division, so that
the other end falls somewhere in the first division against the tenths of a
kilometre.
The total distance is found by reading the whole divisions and adding
the tenths measured in the first division from right to left.
SLIDE 6/3
When using Series M726 care must be taken to use the correct scale
line, because there are the following three scale lines shown on the map:
Kilometres, Statute miles and Nautical miles.
MEASURING
STRAIGHT LINE
DISTANCES BY
PAPER (DIRECT
DISTANCES)
Straight line or direct distances can be measured with a piece of paper,
by laying the edge of the paper between the two end points of the line
on the map, and marking the ends on the paper with a pencil.
SLIDE 6/6
The paper can then be laid along the scale line to obtain the ground
distance.
SLIDE 6/7
Demonstration
Demonstrate measurement of straight line distances on a map using a
paper strip. Include the use of the scale line.
Any Questions
Question from the class.
Practise
Practise the class in estimating and measuring straight line distances on
their map. See Instructors Note
6-3
MEASURING
INDIRECT
DISTANCE BY
PAPER
When planning a route on roads or cross country it may be necessary to
measure indirect distances along roads and tracks. This can be done by
using the edge of a piece of paper as follows:
With a pencil, mark the start point on the paper and place it on the start
point on the map with the edge of the paper along the first part of the
route.
SLIDE 6/4
Where the route bends, hold the paper on the map with the point of a
pencil and carefully pivot the paper until the paper and the next section
of the route are in line.
SLIDE 6/5
Carry on until the end of the route is reached and then measure the total
distance between the two end pencil mark against the scale in the same
way as you did with straight line distances.
Demonstration
Demonstrate measuring an indirect distance to the class, using a paper
strip, map and pencil.
Demonstrate measuring twice, once from each end of the route, as a
check against mistakes.
Any Questions
Questions from the class.
Confirmation
Practise the class in measuring indirect distances on their map. See
Instructors Note
END OF LESSON
Any Questions
Questions from class on whole lesson.
Test on the Whole
Lesson
Give the students a number of direct and indirect distance problems to
work out on their own map.
Make sure everyone starts and finishes on the same point of detail by
giving six-figure grid references of the start and finish.
See Instructors Note
Carefully supervise the student's work.
Pack Equipment
Pass answer papers to the front.
Hand in stores.
Summary
Look Forward
You have been shown three methods of measuring distances:
1.
“Eyeball” estimation using grid lines and diagonals for
approximate results.
2.
Measuring straight line distances with paper and pencil.
3.
Measuring indirect distances along routes using paper and pencil.
In the next Map Reading lesson you will learn about directions on the
map and in the field.
6-4
INSTRUCTORS NOTES
1.
Instructors must select a number of both straight line and indirect distances to be
measured before starting the lesson. For each distance they must have the grid reference
on the start and finish points and the checked distance.
2.
For student testing, the accuracies are:
Straight line + 200 metres
Indirect line + 300 Metres
(However, +100 metres and + 200 metres should be possible on the map - remembering
that map drawing and scale are the largest factors in inaccuracies on the map.)
6-5