Map Reading

SECTION-1

INTRODUCTION TO MAP AND

CONVENTIONAL SIGNS

Ques 1. What is a map?

Ans - A map is representation of selected natural and man made features of the whole or part ofthe earth's surface on a flat sheet of paper on a definite scale and in their correct relative geographic positions and elevations.

Ques 2. What is conventional sign?

Ans - Conventional signs are symbols used to represent certain artificial or natural features/ objects on the map. They are seldom drawn to scale.

SECTION-2

SCALES

Ques 1 - What is scale?

Ans - By scale it means the proportion which the distance between two points on the map bears to the distance between the same two points on the ground

Ques 2. What are the common scales used in survey of India maps?

Ans - (a) 16 inches to 1 Mile 1/3960

(b) 4 inches to 1 mile 1/15840

(d) 1 inch to 1 mile 1/63360

(e) Â½ inch to 1 mile 1/126720

(f) Â¼ inch to 1 mile 1/253440

(g) 16 miles to 1 inch (Approx) 1/1000000

(h) 32 miles to 1 inch (Approx) 1/2000000

SECTION 3

TOPOGRAPHICAL FORMS AND TECHNICAL TERMS

Ques 1. Define important technical terms used in map reading?

Ans (a) Bearing - The angle formed by a line joining two points and the North and South line.

Bearings are always measured clockwise.

(b) Bench Mark - A permanent mark usually cut into a wall recording exact height for future

reference, marked BM with the height on Ordnance Survey Maps.

sea level.

(d) Gradient - The slope of a hill expressed as a fraction.

(e) Grid Lines - Lines running parallel to and at right angles to a North and South

line through approximately the centre of the area covered by the grid system.

(f) Grid North - Except through the origin, grid lines do not lie true North and South or

East and West, Grid North is the direction of the North South grid lines on a map.

(g) Magnetic - The difference between true North & Magnetic Variation North.

(h) Setting - Placing a map so that North on the map points toward the North so that the

objects on the map are placed in relationship to the same objects on the ground.

(j) Trig Point - A point fixed during the triangulation at the beginning of a survey, marked on

Ordance Survey Maps by a small triangle with the height.

(k) True North - The direction of the North Pole from the point.

Ques 2. Define important Topographical terms used in map reading?

Ans . (a) Basin - An area of fairly level ground surrounded by hills or the area drained by a river

and its distributaries.

(b) Col or Saddle - A narrow ridge of high land joining up to higer hills.

mountains from which the ground slopes down in opposite directions.

(d) Dead Ground - Ground which by reason of undulations or hills is not visible to the

observer.

(e) Defile - Any feature whether natural or artificial which could cause a body of troops to

contract its front. An example of a natural defile is mountain pass while a bridge is an

example of an artificial defile.

(f) Escarpment - The steep hill side formed by a sudden drop in the general ground level

usually from a plateau.

(g) Knoll - A small isolated hill.

(h) Plateau - A table land, an elevated region of considerable extent generally fairly level.

(j) Ridge - The line along a hill or range of hills or mountains from which water flows in

opposite directions, a divide, sometimes and the crest of a line of hills as it appears along

the horizon.

(k) Watershed - The line separating the water flowing into two different river systems, the

edge of a river basin.

SECTION-4

THE GRID SYSTEM

Ques 1 - Define grid line?

Ans - A map is covered with a net work of purple lines, some running North and South and other West and East. These form a series of small squares all over the map. These lines are known as 'Grid Lines'.

Ques 2 - What are the basic rules for giving grid reference?

Ans - (a) A reference must always contain an even number of figures. In the normal method, it

will contain six figures.

(b) Always count along the EASTING lines first from WEST to EAST and then from

SOUTH to NORTH, along NORTHINGS.

(c) For the six figures reference, the third and the sixth figure represent the divisions of 1000 yards square to the nearest 10^th part, so they have to be estimated and for these figures a slight latitude is allowed.

(d) If a general grid reference is to be given or there is only one such object in one

square e.g. bridge, temple, road, junction, then a four figure grid reference would suffice.

SECTION 5

RELIEF CONTOURS AND GRADIENTS

Ques 1 - Define Relief?

Ans - Relief is a name used to describe the rise and fall of the ground or in other words the hills and valleys.

Ques 2 - Define Vertical interval, Horizontal equivalent and gradient.

Ans - (a) Vertical Interval(VI) - The rise between successive contour lines is known as the

vertical interval. On map scale 1 inch to 1 mile, the VI of each contour line is 50 feet while

on the Â¼ inch to a mile it is 250 feet.

(b) Horizontal Equivalent - The distance measured flat on the map between adjacent contour lines is horizontal equivalent (HE).

(c) Gradient - A gradient is a slope expressed as a fraction. If we say that a slope has a gradient of 1 inch to 7 we mean for every 7 feet of horizontal distance the slope rises or falls 1 foot vertically. Simple Formula is VI/HE = Gradient. The horizontal equivalent is obtained by measuring on the map and vertical interval by subtracting the contour heights.

SECTION 6

CARDINAL POINTS AND FINDING NORTH

Ques 1 - What are various types of North?

Ans - (a) True North - The direction of North pole from the observer.

(b) Magnetic North- It is the point to which an accurate compass needle points, when

freely suspended.

SECTION-7

TYPE OF BEARINGS AND USE OF SERVICE PROTRACTOR

Ques 1 - Define various types of bearings?

Ans - (a) Bearing - The clock wise angle formed by a straight line joining two points and direction of NORTH, is called the bearing between the two points. A bearing is always measured clockwise.

(b) Grid Bearing. Measured on the map from the Grid North by the help of a protractor.

(d) True Bearing. Calculated by finding out the relation of true NORTH and Grid NORTH or Magnetic NORTH.

Ques 2. How too convert magnetic bearing to a True bearing?

Ans - Suppose the bearing of a certain point P is measured with a compass and is found to be 160 Degrees. First draw a vertical line to represent Magnetic North (because it is a magnetic bearing which is being considered). Next draw a line to P at an angle of 160 degrees. It is only a rough diagram, and the angle can be judged by eye. Thirdly, draw in the true North line approximately 11 degrees East of Magnetic North, with this diagram it becomes clear that true bearing (marked with a dotted line) is smaller by 11 degrees. Therefore, the true bearing of P is 149 degrees.

Ques 3. How too convert magnetic bearing to a True bearing?

Ans - Measuring with a protractor on the map, the bearing of a Wind Mill at Y from a Church at Xis found to be 120 degrees. To convert this grid bearing to a magnetic bearing, draw a diagram as under, this time starting with the Grid North line. Since the magnetic bearing is larger than the grid bearing by 11 degrees and it is therefore 131 degrees.

Ques 4. What are the usage of service protector?

Ans - (a) Plot and measure bearing on paper or on a map. For bearing between 0 and 180 degrees their Zero edge must be on the LEFT and for 180 degrees -360 degrees it must be on the RIGHT.

(b) Measure distance in inches correct unto 1/100^th.

(d) For using the diagonal scale one must use an intermediate agent. Mark off the distance to be measured on the straight edge of a paper or by means of a divider and then put the paper or divider on the diagonal scale and measure.

SECTION-8

PRISMATIC COMPASS, ITS USE AND

INTRODUCTION TO GPS

Ques 1. What are the types of compass?

Ans - Compass is of two types as under : -

(a) Dry Type

(b) Liquid Type

Ques 2. What are the various parts of a liquid compass?

Ans These are as under: -

Ques 3. What is Global Positioning System (GPS)?

Ans GPS is a system of satellites and receivers that allows people and devices to pin point their precise location on the earth. The normal GPS operational constellation consists of 24 satellites that orbit the earth in 12 hours.

Ques 4. What are the usage of GPS?

Ans - (a) Used by fishermen and hikers.

(b) Used by civilian & para military vehicles to navigate their route.

(d) Used in defense in battle fields and insurgency-affected areas.

(e) It assists troops to navigate in thick jungles, mountains and deserts.

(f) GPS is also used to guide missiles to pre specified targets.

SECTION-9

SETTING A MAP, FINDING OWN POSITION AND NORTH

Ques 1. When is a map is considered to be set?

Ans - A map is said to be set or oriented when it is placed such that it corresponds directly with the ground i.e. when true NORTH on the map points to true NORTH on the ground.

Ques 2. What are the various methods to find North?

Ans - (a) Watch method.

(b) By stars

(d) From Sun

(e) Compass

(f) GPS

SECTION-10

MAP TO GROUND

Ques 1. What are the methods used to identify objects from Map to ground?

Ans - (a) Bearing and Distance Method. With the help of bearing and distance, find out own position. Find out the distance of the object to be identified on ground with the help of a scale on the map. Using service protractor, find out the bearing of the object and convert it into magnetic bearing. Set the magnetic bearing on compass and look for the object in the given bearing. Estimating the distance on ground, the object will be identified.

(b) Direction and Distance Method. Draw a line on the map between own position and object to be identified. Calculate its distance and using any of the following methods find the direction of the object:-

(i) With the help of a sight rule find the ground direction of the object.

(ii) With the help of two points on the map estimate the ground direction.

(iii) Place a foot ruler /pencil at own position and align it with line of the map.

(iv) Place a pin each at own position and at the object on the map. Align both

pins and find general direction.

(c) By Estimation Method. In this method measuring bearing, distance and direction, object is identified with the help of other details in the proximity of the object.

SECTION-11

GROUND TO MAP

Ques 1. What is the intersection method of identifying objects from ground to map?

Ans - Intersection Method. To find out the objects which are at a larger distance or in hilly terrain, intersection method is used. In this method help of minimum two prominent objects are taken which can be easily identified on the ground. Lines are drawn from the prominent objects to the object to be identified on map. This method is used when we cannot estimate exact distance. Intersection is done in two ways:-

(a) By Compass Bearing. Take the bearing of the object from two known prominent objects. Draw the lines on the map. The object will be in the proximity of the intersection of the two lines. Magnetic bearing is found by two methods:-

(i) By Compass. Take the forward bearing from known object.

(ii) By Back Bearing. In war, in case we intercept the enemyâ€™s transmission, with the help of the fall of the shot we can find out the location by working out back bearing.

SECTION-12

POINT TO POINT MARCH

Ques 1. What is night march?

Ans - When a navigation party moves at night with the help of compass and night march chart, this is called night march.

Ques 2. What all items are required by navigation party?

Ans - (a) Set compass as per bounds.

(b) Luminous stick.

(d) Marching chart.

(e) White lime/ chalk.

(f) Stone pebbles for measuring steps.

(g) Frosted torch.

Ques 3. What is the composition of navigation party?

Ans - (a) Guide. He carries a luminous stick and a compass set to a given bearing.

(b) Assistant Guide. He has a white piece of cloth at his back for identification and a stick to measure depth of nala / pits.

(c) Recorder. He carries additional compass already set on given bearing, night march chart and stone pebbles. He measures the distance.

(d) Scouts. Number of scouts could be from 2 to 4 depending upon the route and tasks.

Ques 4. What points should be kept in mind by all members of navigation party?

Ans - (a) While marching do not cough, talk or make any noise.

(b) While marching keep inter person distance in mind.

(d) Smoking / using any kind of light is strictly prohibited.

(e) To read night march chart use frosted torch.