Map Reading

THE BASIS OF MAP READING Introduction Elements of a map Grid systems and map references Map scales and distances Directions and bearings Setting a map Identification of own location

INTRODUCTION The main aim of this lesson is basically to give cadets information on the basis of map reading. This is to help them in their orienteering practices/competition. What are maps? Maps are graphic representation of the Earth’s surface that are drawn to scale on a flat surface.

MAPS Physical Environment Human Environment Land masses and oceans Major landforms Major drainage systems Components of climate Global vegetation patterns Agricultural patterns Industrial patterns Settlement patterns Communication patterns

Elements Of A Map Title Scale Legend Grid Lines North arrows

Grid Systems & Map References 10 70 60 50 50 40 40 30 30 20 EASTINGS NORTHINGS

The North to South grid lines are called EASTINGS whereas the East to West grid lines are called NORTHINGS. A grid square can be named 4 grid reference (2030) 6 grid reference (204305) 8 grid reference (20443050) 40 30 20 30

Map Scales & Distances A scale is the ratio between a given map distance and the actual ground distance. Type of scales: Statement Linear Bar As a representative fraction

How to measure distance on a map? Straight line distance Using ruler or a pair of dividers Curved distance Using ruler (Break the curved distance into small straight pieces) A thread

Direction 4 Cardinal Points North, South, East and West Further divided in 16 divisions Etc. North-East, North north-East… Each division is approximately 22.5 degrees or 500 mils

True North- the direction of the Earth’s North Pole which is 90 degrees North. The North pole star is directly above the North Pole. Magnetic North- the direction of the Earth’s Magnetic pole, i.e. the direction in which the needle of a compass point. Grid North- the direction of the vertical grid lines called eastings . Note- All three North do not point at the same direction.

Bearings Equipment Compass, protractor Back bearing If the direct bearing is between 0 to 180 (degrees) or 0 to 3200(mils), add 180 (degrees) or 3200 (mils) to obtain the back bearing. If the direct bearing is between 180 to 360 (degrees) or 3200 to 6400(mils), subtract 180 (degrees) or 3200 (mils) to obtain the back bearing.

Place the map in a horizontal position. Place the compass parallel to a north-south grid line with the cover side of the compass pointing towards the top of the map. This will place the black index line on the dial of the compass parallel to grid north, we have a magnetic variation on the face of the compass formed by the index line and the compass needle. Rotate the map together with the compass until the variation formed by the black index line and the compass needle matches the deviation shown on the declination diagram printed on the margin on the map. The map is then orientated. In Singapore, because the deviation between the grid north, true north and magnetic north is very slight, you need not be concerned about the magnetic variation. You need only to rotate your map until the compass needle points towards grid north.

Known Location & Known Point Method Draw a straight line on the map joining your location with the known point. Rotate the map until the line points towards the known points on the ground. Demonstrate: As an example, our position is on OCS HQ Building MGR 3185 4750. The known point is NTU road junction reflected in the map at MGR 316 483. You need to draw a straight line on the map from OCS HQ Building to NTU road junction. Once this has been completed, rotate your map until the line that you have drawn points towards NTU road junction as seen from your position. The map is then set.

Resection With Compass Known location B Known location A Unknown Known location C location X

Resection With Compass Known location B Known location A back azimuth (a) Unknown Known location C location X

Resection With Compass Known location B Known location A back azimuth (b) ideal angle 1600 mils Known Known location C location X

Resection With Compass Known location B Known location A back azimuth Known Known location C location X (c)

Resection With Compass Known location B Known location A triangle of error Known Known location C location Y

Resection Without Compass ( Straight Edge Method )

direction of move pylon known location bridge stream Known Line and Distance From A Known Feature

Known Line and Distance From A Known Feature direction of move pylon known location x bridge 200m 1500mils stream

direction of move pylon known location bridge 150 m 200m 1200 mils 1500mils stream Known Line and Distance From A Known Feature y

Direction of move Known feature Unknown own location Known Line and Azimuth From A Known Feature

Direction of move Known (a) feature grid azimuth - 700 mils Unknown own location Known Line and Azimuth From A Known Feature

Direction of move Known feature back azimuth Unknown own location Known Line and Azimuth From A Known Feature SLIDE 14/8c

Direction of move Known feature Known own location Known Line and Azimuth From A Known Feature

a. Intersection b. By azimuth and distance METHODS OF IDENTIFYING OTHER LOCATIONS

INTERSECTION Unknown location X Known location A Known location B Known location C

INTERSECTION grid azimuth Unknown location X Known location A Known location B Known location C (a)

INTERSECTION Known location X Known location A grid azimuth Known location B Known location C (b)

INTERSECTION Known location Y Known location A grid azimuth Known location B Known location C (c)

BY AZIMUTH AND DISTANCE Unknown location X Known location A

BY AZIMUTH AND DISTANCE Unknown location X grid azimuth Known location A (a)

BY AZIMUTH AND DISTANCE Unknown location X Estimate distance - 500 m Known location A

BY AZIMUTH AND DISTANCE Known location X Known location A

CONCLUSION 1. Method of identifying own location : a. Resection b. By known line and distance from known feature c. By known line and azimuth from known feature

2. Methods of identifying other location : a. Intersection b. By azimuth and distance CONCLUSION

Pacing Pacing help us to judge how much distance we have covered. Two ways Single step Double step

Pacing Counting a double pace is easier than counting every single pace. On a fairly level ground, paces determine distance as follows: 65 to 75 paces per 100m for men 80 to 90 paces per 100m for women Pacing also depends on the terrain. i.e. fairly level ground, upward slope, downward slope. Should we get lost or things do not follow as plan, we can roughly know the distance that we have covered.

END Prepared by 2LT Muhd Nazir

Map Reading

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Map Reading