01 Toposheets - Lets start all over again INTRODUCTION TO TOPOSHEETS -1

INTRODUCTION TO TOPOSHEETS-1

Dear student,
Welcome to my blog!  Many students from all over India have requested to update my blog. So I have decided to update my lessons on toposheets. I'm using very simple language to explain this lesson.
Lets begin.

WHAT IS A MAP? 

* Its a pictorial representation of the earth. It is a part or whole of the earth’s   surface.

•It is drawn to scale, on a flat sheet of paper

ELEMENTS OF MAP

A   A MAP has 5 elements.

1.Title

2.Scale

3.Grid

4.Direction

5.Key

1. TITLE

• It Represents

a) Name of the region depicted

b)Theme of the map

•Example

–INDIA (Name of region)

–PHYSICAL (Theme of the map)

2. SCALE

•Ratio

Ratio is the distance between two places on map and distance between same two places on ground

•It can be expressed as

i) Statement (2 cm = 1 km OR   2 cm to 1 km)

ii) Representative Fraction

  (1:50000)

Representative Fraction (R.F. )  is also called as numerical scale. It is expressed as a ratio of map distance and ground distance. 

For example 1:1,000,000 means one unit of distance on the map corresponds to 1,000,000 units of distance on the ground. The advantage of R.F. is that it can be used universally irrespective of the local unit of measurement of distance. The map can be reduced or enlarged without changing the R.F.

iii. Linear Scale or Graphical Scale: 

This scale is expressed as a horizontal or straight line.The base is calibrated to express visual equivalents of representative fraction or verbal scale. The bases are divided into a number of equal parts and are marked to show what these divisions represent on actual ground. The scale has the advantage that it remains true even after reduction or enlargement of the map. However, it is useful only to those who are familiar with the particular unit of measurement.

Understanding Scale

•Scale

                Distance between two places on map (a)
         Distance between the same two places on ground (b)

Scale is the relationship between the distance on a map and the real distance on the earth’s surface.

Statement to R.F.

•If a = 2 cm; b = 1 km

then 

•Scale = 2cm / 1 km   

OR

2 cm / 1 X 1000 X 100 cm  

OR

1 cm / 50000 cm  

OR

1 : 50000

Distances on the map are smaller than the 

corresponding distances on actual ground. Scale is the 

means which enables us to reduce the whole or a part 

of the earth to a size which is not only convenient and 

handy but also logical and scientific. A general 

definition of scale is that it is a ratio between the 

distance on a map and the corresponding distance on 

the earth. For example if two points located 10 km apart 

are shown 1 cm apart on a map, then the scale of the 

map would be 1 cm to 10 km. It may also be converted 

into R.F as given below.Suppose, 1 cm = 10 KM.

MAP DISTANCE
_______________
GROUND DISTANCE
=
1 cm
_____
10 km
=
1 cm
____________
10 X 10,000 cm
= 1: 1,000,000
(Note: 1 km has 100,000 cm.)

Methods of Measuring Linear Distance

Linear distance on maps are of two types:

(i) Straight lines like roads, railway line, and canals;

(ii) Curved or Zigzag lines, showing streams, coastline etc.

(a) When the line is straight, the distance can be measured with the help of a divider.Open a pair of dividers and place one of its legs at one end of the straight distance and the other leg on the other end on the map. Then lift the divider and place it on the calibrated bar scale to get the distance on the ground.

(b) When the route is zigzag, place one end of a thread at the starting point and carry the thread along the line. After completing the distance stretch the thread and measure the length. It will give approximate distance.It can also be measured with the help of a plain divider, as explained earlier, but the measurement will be less accurate. It can also be done with the help of a strip of paper.

I hope you understood !  

We covered two points so far. A map has a title and it is drawn to the scale. Check the atlas.  Study any map, be it physical, or political.

Did you go through the map? I hope so. Did you find the TITLE and SCALE? I hope you did.

Shall we continue?

3. Grid

GRID:  A grid is a rectangular square system of lines superimposed on a map, within which any point can be located.

North / South lines are called Eastings because the numbers increase as they go East.
•East / West lines are called Northings because the numbers increase as they go North.

It is a set of

–Vertical lines

–Horizontal lines

* Examples

•Latitudes & Longitudes

•Northings & Eastings

Grids are used to locate places

•Draw an area to proportion   on map

•Could be used to  determine area

What are Eastings and Northings?

1.Eastings run – move left to right; and

2.Northings run – bottom to top.

What are the two most important things to remember when giving a grid?
1.Easting value first; and
2.never round up.

4. Direction

Direction has been defined as an imaginary straight line on the map or the ground showing the angular position of various maps with respect to a common base direction. The line pointing to the north is regarded as the zero direction or base direction line.A map must have the base directions represented on it to enable the user to locate different features with respect to each other. North, south, east and west are the four major directions. These are also called cardinal points. In between cardinal points one may have several intermediate directions.

•Angular distance

–From observer’s position

–To any place on map

–With respect to NORTH

  (Position of Pole Star)

•Can be expressed as

–Conventions (N, S, E, W, etc.)

Bearing OR Azimuth (Angle)

5.Key or Legend

Every map contains a legend or a key. It lists the features and the signs

or symbols used in the map for showing these features. As you know 

various types of features or phenomena are represented on maps. They 

relate to both land and sea and are shown with the help of conventional

signs and symbols. The signs and symbols include lines, icons, alphabets, 
shadings and colours. As a convention, specific colours show certain area 
features.

It is a set of

–Colours

–Symbols

–Shading patterns

•Used to depict ground  features on the map

For example: See the Key(Legend) below

Let's revise.

 A map has 5 elements. Go through your Atlas. 
 It has 
 1.Title 2.Scale 3.Grid 4.Direction 5.Key

 Now we will study about Topographical Survey Map.

How is a Topographical Map different?

What is a topographic map?

A topographic map is a detailed and accurate graphic

 representation of cultural and natural features on the ground.

Features of Topographical Maps

•Height (and it distribution)   is shown using contours

•Helps one to visualise the   pattern of unevenness

  (topography) of the land

•Large scale map

–Minute details are included

–It covers a smaller area

•It could be used for a number of purposes

–Millitary

–Building bridges, roads, railways, dams, canals, etc

–Research (geology, botany, etc.)

-  any type of geographic planning or large-scale architecture; 

- earth sciences and many other geographic disciplines; mining and other earth-based endeavours;

- and recreational uses such as hiking or, in particular, orienteering, which uses highly detailed maps in its standard requirements. 

Showing Topography using hachures + contours

•Map conventions

The various features shown on the map are represented

 by conventional signs or symbols. 

For example, colors can be  used to indicate a classification of

 roads. These signs are usually explained in the margin of the

 map, or on a separately published characteristic sheet.

•Topographic maps are also commonly called contour maps 

or topo maps. 

•Topographic maps conventionally show topography, or land

 contours, by means of contour lines. Contour lines are 

curves that connect contiguous points of the same altitude 

(isohypse). In other words, every point on the marked line of 

100 m elevation is 100 m above mean sea level. 

Understanding Topographical Maps

•Understanding of surface depends on the ability to interpret

topo maps.

They-

• are based on accurate surveys.

• show a variety of landforms with carefully chosen symbols 

& signs.

•shows natural features like hills, valleys, waterfalls,

•also show man made features like roads, railways, buildings, 

bridges and canals

INTERPRETATIONOF TOPO MAPS AND SURVEY MAPS

•It involves ability to follow the symbols portrayed in the 

map.

•Understand the information given in pictorial and written 

form

•Visualize the topography of the original area by interpreting 

the contour

•Spot heights skillfully

•Map reading is a practical skill.

•Can be developed only by reading topo map very minutely 

and mentally analyzing the details with the help of 

conventional signs & symbols given in their conventional

colours

1.Identification of topographical maps

2.Reading the Grid reference

3.Scale (R.F.)

4.Representation of Relief by contours

5.Directions

6.Measuring distances and calculating distances

7.Drainage

8.Man-made and natural features

9.Means of transport in relation to relief

10.Land use and irrigation

11. Settlements

12. Inferring occupations 

13. Importance of colours and tints in topographical 

survey sheets 

14. Legend 

15. Glossary of conventional signs and symbols used in

survey maps

1. INFORMATION IN THE MARGINS

1.Information in the Margins:

i)The number of the topo sheets: Topo sheets numbers 

can give an idea as to which part of India is shown on the

 map.

  For example, topo sheet numbers 45D/7, 45D/10 and 45 F/3 show parts of Gujarat and Rajashthan.

ii) Latitudinal and Longitudinal extent: These indicate in which part of the Earth the area is located.

•Knowing the number of toposheet can give us a clue about 

the general physical relief of the region  and its climate which

 can be confirmed by other information given in the map.

•Example

- Since all toposheets are from India, it may  be inferred that 

all the regions represented  by those topo sheets would have

 a tropical monsoon climate, with seasonal rainfall.

•Western Rajasthan – You may expect scanty rainfall- a fact

 which could be verified by the  presence of dry river beds

 and disappearing streams.

45D/7 shows a region of northern Gujarat,  closer to the 

border of Rajasthan

•45D/10 lies in the southern part of Rajasthan close 

to the border of Gujarat region

•45F/3 lies in the western Rajasthan, near Jodhpur

•53B/7 shows a region in Punjab, close to the border 

of Haryana.

•64P/13 shows a region in north-east Orissa

Title of Topographical Maps

For example:

•45 D/7

•45 D/10

•67 F/9

Does it make any sense?

No??? Didn't get it????

Don't worry! We will do it again!

Bifurcation of Toposheet

i)The number of the topo sheets: Topo sheets numbers can give an idea as 

to which part of India is shown on the map. 

For example, topo sheet numbers 45D/7, 45D/10 and 45 F/3 show parts of 

Gujarat and Rajashthan.

2. READING OF GRID REFERENCE

•A Grid is a set of lines used to find the exact location of places on a map.
•The National Grid Reference is a system of rectangular co-ordinate.
•The origin of the grid reference lies at a point in the south-west corner of the map.
•Thus any place on the map can be located by starting its distance east or north of the origin of the grid reference.
•Topo maps bear the national grid of squares drawn to the scale of 2 cm=1km with each square having a side measuring 1 km.
•These are sheets most commonly used for various purposes and are of vital practical importance.
•Vertical lines=Eastings since they are numbered from west to East
•Horizontal lines = Northings - they are numbered from South to North
•Net work of horizontal and vertical lines or the Eastings and Northings , is called the Grid.

Confused? Too much of theory?

Let's do it again!

See the picture below.

GRID REFERENCE

1. Relative Location

§Location expressed using landmarks

▪Behind Big Bazaar

▪Opposite Shiv Temple

▪Near Patel Pan

2.Absolute Location

§Location expressed using known

  grid system

▪19° N; 78° E 

GRID SYSTEM USED IN TOPOGRAPHICAL MAPS 

1. Latitudes and longitudes

2. Eastings and Northings

•A Grid is a set of lines used to find the exact 

location of places on a map.

•The National Grid Reference is a system of 

rectangular co-ordinate.

•The origin of the grid reference lies at a point 

in the south-west corner of the map.

•Thus any place on the map can be located by 

starting its distance east or north of the origin 

of the grid reference.

See Eastings and Northings in this map

Topo maps bear the  national grid of squares drawn to the 

scale of 2 cm=1km with each square having a side 

measuring 1 km.

•These are sheets most commonly used for various purposes 

and are of vital practical importance.

•Vertical lines=Eastings since they are numbered from west 

to East

•Horizontal lines = Northings - they are numbered from 

South to North

•Net work of horizontal and vertical lines or the Eastings and 

Northings , is called the Grid.

•It is also identified as the Grid Reference.

READING THE GRID REFERENCE

i)Origin is the South –West (SW) corner of the map. The reading on the map is always taken with reference to this origin.
ii)Eastings are always read to the East of the origin.
iii)Northings are always read to the North of the origin.
•It is also identified as the Grid Reference

i)The readings are always taken to the right of the Eastings and to the North of the Northings.
ii)While giving a grid reference, Eastings are always stated first, followed by Northings

4 FIGURE GRID REFERENCE

In four-figure grid reference, the first two figures are the 

eastings and the last two are the northings

So remember, in Four Figure Grid Reference

¡First two digits are eastings

¡Next two digits are northings

¡By convention, lesser value is always taken 

How did we get the 4 figuure grid reference?

Check the map below.

1) Find the Four Figure Grid Reference of RAMPURA.

 First, locate Rampura. See RED SETTLEMENTS

Move from West to East. 

Rampura settlements begins after the Easting 95 

So Easting is 95

Then move from South to North (Northings)

Rampura Settlement begins just after Northing 80

So Northing is 80

So 4 Figure grid reference of Rampura is 9580

2) Find the Four Figure Grid Reference of ARNWADA.

First, locate ARNWADA. See RED SETTLEMENTS

Move from West to East. 

Arnwada settlements begins after the Easting 94 

So Easting is 94

Then move from South to North (Northings)

Arnwada Settlement begins just after Northing 81

So Northing is 80

So 4 Figure grid reference of Arnwada is 9481

Few examples to make you clear!

SMALL TEST

Did you cheat?

Now check your answers!

Did you get all the answers right? Yes? Did you cheat?

Ok, Don't scream at me! I believe you.
  Let me check again! Do this work sheet

Write your answers in the comment!

SIX FIGURE GRID REFERENCE

Four figure grid references are indeed very useful. However, a major 

weakness of four figure grid references is the fact that they are not very 

accurate. All objects in the same grid square have the same four figure 

grid reference even though they may be hundreds of meters apart . When 

greater accuracy is necessary, a six figure grid reference is used. A six 

figure grid reference does not only indicate the grid square an object is 

located in, it also tells us the exact point within the grid square where the 

object is found. Therefore, objects located in the same grid square will 

have the same four figure grid reference, but different six figure grid 

references.

How to Give a Six Figure Grid Reference?

EE represents Easting,  NN represents Northings.

A six figure grid reference takes the form EEXNNY.  EE and NN represent 

four figure grid reference for the object in question. X is a digit which tells 

us how close to or far away from the easting the object is located. The 

higher the number, the farther away from the easting the object is. 

Similarly, Y is a digit which tells us how close to or far away from 

the northing the object is found. X and Y can have a value ranging from 

zero to nine. 

So remember:

For greater accuracy, a third figure may be added to 

two-figure eastings and northings.

i) Obtain the four figure reference by using first 

    two digits of eastings and northings.

ii) Then divide each kilometre into ten parts visually, both 

    vertically & horizontally.

iii) Mark the division of eastings and the division of the northing corresponding to the location.

iv) The crossing point is the location of the reference point

Look at the grid square below. Look at the letter “A” located 

within the square. The four figure grid reference for “A” is 2345. 

However, 2345 is also the four figure grid reference for any object 

which lies anywhere in this grid square. We can give the exact 

location of this “A” by giving a six figure grid reference. Let us take it 

step by step.

Step 1

Remember a six figure grid reference takes the form EEXNNY. The first two digits represent the easting immediately to the left of the object. The easting to the left of “A” is 23, therefore we have our first two digits. The third digit (X) represents the distance between easting 23 and “A”. To determine this we need to divide the space between easting 23 and easting 24 into ten equal parts as seen in the diagram below.

The lines are parallel to our easting are an equal distance apart from each other. Let’s call these lines “mini eastings”. Now we need to count the number of mini eastings that are between easting 23 and “A”. In this case there are four. Therefore our third digit is 4. So the first part of our six figure grid reference is 234.

Step 2

The fourth and fifth digits in a six figure grid reference represent the northing which is directly under the object. In this case it is northing 45. The sixth digit tells us the distance between northing 45 and the object. We must divide the space between northings 45 and 46 into ten equal parts as seen below.

Once again the lines are parallel to northing 45 and are an equal distance apart. Let us call these lines “mini northings”. We must count the number of mini northings which are between northing 45 and “A”. In this case there are seven of them. Therefore 7 will be the last digit in our six figure grid reference. The second part of our grid reference is 457.

Our entire six figure grid reference is 234457. Remember:

• the first two digits represent the easting immediately to the left of the object( in this case easting 23).
• the third digit (4) represents the distance between the easting and our object. In this case the object is roughly four tenths of the distance between easting 23 and easting 24.
• the fourth and fifth digits represent the northing directly under our object (in this case northing 45)
• the sixth digit represents the distance between the northing and our object. In this case, the object is roughly seven tenths of the distance between northing 45 and northing 46.

Note: If the position of “A” was such that it lay directly on mini easting 4 or mini northing 7, its six figure grid reference would still be 234457. 

The two steps shown above need not be done separately. Your “mini eastings” and “mini northings” can be drawn such that they form a smaller grid inside the grid square in which the object is located. The six figure grid reference can be completed by giving the number of the mini easting immediately to the left of the object and the number of the mini easting directly under it (see below).

The six figure grid reference is 234457

Find the six figure grid reference of temple

3. SCALE

Dear friend,

We have already done with SCALE.  Let's do it again. 

Refer to Survey Map No. 45D/7
•In the map, 1:50,000 is the R.F. of the map, which means that one unit on the map represents 50,000 units on the ground.
•For example, 1 cm on the map represents 50,000 cm on the ground.

(Scale of this toposheet is)
Scale-2cm:1 km or 1:50,000

Scale is a RATIO 

     Distance between two places on map (a)  

Distance between the same two places on ground (b)

•It can be expressed as1.Statement (2 cm = 1 km OR 2 cm to 1 km)2.Representative Fraction (1:50000)3.Linear Scale

Statement to R.F.

•If a = 2 cm; b = 1 km

•Scale = 2cm / 1 km  

OR

2 cm / 1 X 1000 X 100 cm 

OR

1 cm / 50000 cm 

OR

1 : 50000

R.F. or Representative Fraction is the ratio between the distance on the map and the corresponding distance on the ground in the same unit.

•Therefore, R.F.

Distance on the map

___________________

Distance on the ground

In the above map, R.F. = 1:50,000

This map is referred to as 1:50,000 map and its scale is 2 cm=1 km.

4.Representation of Relief by contours

CONTOURS

What are contours?

•A contour is a line on a map joining two points of equal height, and is the standard method of showing relief on a topographical map.

CONTOUR INTERVAL: The difference of elevation between two successive contours. Contour interval on the toposheet is 20 meters

Please Note:

Contours are shown at regular vertical intervals.

• On a 1:50,000 map the interval is 20 m.
  

Characteristics of Contours

•All places on the contour line lie at the same elevation

•Contours never intersect each other

•Contour interval (difference between two successive 

contour values) is uniform throughout the map

•All contour values are multiples of the contour interval

•Height of any place on map can be determined

 Spacing between contours

•Widely spaced contours –Gentle slope

•Closely packed contours –Steep slope

•Overlapping contours –Vertical slope

 Visualisation

  INTERPRETATION OF CONTOURS

•The shape of the contours indicates the shape of the ground.

When contours are further apart, the slope is gentle and when contours are close together the greater the drop.

When contours are equal distance apart,  the slope is uniform:

a.Contours are continuous. No matter how far they travel, they always return to where they started. Except for a cliff.

b.When spacing of contours down a slope gets close together at the bottom, the slope is convex.

c. When spacing is further apart, the slope is concave.

Please Note: This lesson will be updated again.

Next topic :
Toposheets - Lets start all over again INTRODUCTION TO TOPOSHEETS -2

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Br. Hector Pinto

St. Joseph's College, Nainital

For detailed explanation, click this link:

https://brhectorsgeoworld.blogspot.com/search/label/A2%20TOPOGRAPHICAL%20SURVEY%20MAPS%3Dpart%201