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UNIT 12
REPRESENTATION OF
CLIMATIC DATA

Structure
12.1 Introduction 12.4 Summary
Expected Learning Outcomes 12.5 Terminal Questions
12.2 Elements of Climatic Data 12.7 Answers
12.3 Representation of Climatic Data 12.6 References/Suggested
through Diagrams Further Reading
Climograph
Hythergraph
Ergograph
Wind Rose or Star Diagram

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You have read climatology in the course on ‘Physical Geography’ in your First
Semester. You might have seen various diagrams and maps namely isotherm,
isobar, line and bar diagram and wind rose etc. Just imagine a situation where
you will be provided with monthly data for temperature and rainfall of ten places
for thirty years, it would be difficult for you to compare and interpret the data.
However, the same data is represented through multiple line diagrams. We are
sure that it would be easier for you to comprehend, compare and interpret.
Therefore, we say visualization is one of the effective methods of
representation of data in general and climatic data in particular.

In this unit, we will discuss about representation of climatic data through

diagrams namely climograph, hythergraph, ergograph and wind rose. Like 195
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previous units, we will explain concept and its uses along with one example
and steps involved in the construction of such diagrams. Once you complete
this unit, you would understand the steps of construction, utility and application
of these climatic diagrams.

In the next unit i.e., Unit-13, we will discuss about representation of climatic
data through maps. We will also explain in detail about representation methods
of geographical data in Unit-14.

Expected Learning Outcomes

After studying this unit, you should be able to:

™ identify appropriate diagrams for representing varied climatic data;

™ describe concepts, methods of construction and their uses; and

™ represent climatic data through appropriate diagrams.

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Before discussing about the representation of climatic data, we should know
the elements of climate on which data is gathered. If you remember, we watch
it on the television, listen it on the radio, read it in the newspapers where it is
presented in the form of weather report. Today, you can also see it in your
mobile phone. Generally, it presents weather condition of past 24 hours and
predicts what would happen in the next 24 hours or more. In that weather
bulletin particularly in newspapers and television, many a time, it is
supplemented by satellite image and diagrams. We are sure that till now, you
might have recollected all the weather or climatic elements we are talking
about. If not, then please read it from newspaper, listen to news bulletin or
watch it from television and revisit the Unit on “Elements of Weather and
Climate” which you have already read in the First Semester Course on
“Physical Geography”.

Most of the weather reports present five major elements of weather namely
temperature, pressure, wind flow, humidity and precipitation. Some aspects of
these five elements are shown in diagrams like line diagram, bar diagram,
wind flow diagram etc., and some of them are presented in the maps like
isotherm and isobar etc. We will discuss about the representation of climatic
data through diagrams in this unit. Representation in the form of isotherm,
isobar, and pressure gradient will be taken up in the next Unit 13 titled
“Weather Maps”.

Let us now discuss in brief about the five climatic elements as mentioned
above.

(i) 7HPSHUDWXUH: The most significant factor that determines weather is

temperature. Temperature is measured using a thermometer in degrees
Fahrenheit or Celsius. We generally represent all sorts of variations
starting from diurnal i.e., in a day, monthly, annual and over a longer
period of time. This provides you the maximum, minimum, range and
average temperature of different places on the globe.
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(ii) 3UHVVXUH: Air pressure or simply we can say pressure has a direct
relationship with temperature. It includes the amount of pressure exerted
by the air in a particular air mass. Air pressure is also called barometric
pressure because it is measured using a barometer and commonly
measured in inches of mercury. You might have seen in weather reports,
it has been depicted in terms of areas of high pressure and low
pressure.

(iii) +XPLGLW\: Humidity is also another important factor that determines the
weather of a place. Humidity is a measure of the water content present
in the air mass. It plays a vital role in weather formation and agricultural
activities etc.

(iv) 3UHFLSLWDWLRQ: You have read various forms of precipitation namely

snow, rain, hailstorm and drizzle etc. As you know, it is one of the
essential elements for survival of the planet earth in general and survival
of plants, animals and human beings in specific. We generally measure
amount of rainfall in a place by using rain gauge.

(v) :LQG: As you know temperature and pressure are the major
determinants of wind flow. Wind speed and direction, gives you an idea
about wind patterns of a particular place. If you remember while
presenting a report about cyclonic storm, the reporter describes the wind
speed as well as direction. This type of data we present through wind
rose diagrams.

After knowing the elements of climate related data, let us discuss briefly about
the instruments used for collecting above mentioned weather related data.
Different types of instruments are used to measure different parameters. As
you already know that thermometer is used for measuring temperature,
barometer for pressure, anemometer for measuring wind velocity etc. Today,
we have automated weather station (AWS’s), in which these instruments are
found at one place and as name suggests weather phenomena are recorded
automatically. You will read more about this in the next unit. Once data is
recorded, these data have to be gathered and communicated to different
stakeholders like farmers, policy makers and general public etc. for different
purposes. While communicating this huge data, we take the help of certain
diagrams to make communication more effective and easily understandable.
What exactly we want to see out of this huge data? We look for trends,
patterns and relationships. Once we understand these three processes, it
would be easy for us and respective stakeholders to draw inferences from
such graphs and diagrams.

There are certain diagrams which are general in nature and represent various
types of data including climatic data. Examples are line diagram, bar diagram,
combined line and bar diagram etc. We will discuss about these diagrams in
Unit 14. But there are certain diagrams which were developed for depicting
climatic data exclusively. Examples of such diagrams are climograph,
hythergraph, ergograph, wind rose and star diagrams etc. We will discuss
about these exclusive diagrams in the next Sections.

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Before that, let us know what we have learnt so far, by answering the
questions as given below.

SAQ 1
Fill in the blanks with suitable words.

(i) Weather bulletin in newspaper and television, many a time is

supplemented by _________________ and _____________.

(ii) Weather phenomena of a place are recorded automatically by

________________________________.

(iii) Communicating huge data with the help of diagrams make

communication more _______________ and ____________________.

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As mentioned above, we will discuss only those diagrams which are
exclusively used for representing climatic data. While doing so, we can define
the month or season and place of interest used for representation of the
weather phenomena. The weather data including past weather conditions and
long-term averages can be used for representation through various diagrams.
Some of the diagrams with the help of which you can represent these data are
given below:

1. Climograph

2. Hythergraph

3. Ergograph

4. Wind rose and Star diagram

Let us discuss these diagrams, their uses and steps involved in the
construction with one example each.

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Climograph or climogram is nothing but the short form of climatological
diagram. This is a twelve sided polygon that represents selected two
climatic elements of a particular station against one another. This twelve
sided polygon or climograph was constructed by taking wet bulb temperature
and relative humidity as indicators for representing climatic condition of a
place.

This was first conceived by J. Ball in 1910 and later expanded and improved by
Leighly (1926), USDA (1941), and Taylor (1949). This diagram was also
extensively used by Koeppen to summarize variations in world climatic
conditions while developing his classification of climatic regions (you have
already read it in a Unit of third block titled ‘climatology’ in first semester

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course). If we look at the history behind the construction of climograph, it was
also used to identify the places on the basis of scale of habitability or
hospitability for white settlers in the tropic regions.

As mentioned above, the sole purpose for which Griffith Taylor constructed
climograph was to identify the places in tropical area that were suitable or
hospitable for white settlers. That is why he coined four special terminologies
for four distinct climatic conditions. These four terms are always mentioned in
the four corners of the climograph. These terms are raw, muggy, scorching
and keen and are marked in South East, North East, North West and South
West corners of a climograph respectively. Let us discuss each term along
with its specified parameters like wet bulb temperature, measures in degree
Fahrenheit (OF), or degree Celsius (OC), and relative humidity as well as the
climatic conditions which it represents. These are as follows:

L 5DZ: Wet bulb temperature below 40OF (4.4OC), and relative humidity
over 70 percent. Therefore, raw represents FROGDQGPRLVWFRQGLWLRQ.
LL 0XJJ\: Wet bulb temperature over 60OF (15.5OC), and relative humidity
over 70 percent. Therefore, muggy represents KRWDQGKXPLG
FRQGLWLRQ.
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humidity below 40 percent. Therefore, scorching represents KRWDQGGU\
FRQGLWLRQ.
LY .HHQ: Wet bulb temperature below 40OF (4.4OC), and relative humidity
below 40 percent. Therefore, keen represents FROGDQGGU\FRQGLWLRQ.

Griffith Taylor has also constructed the scale of discomfort based on his
experience gained from the plotting of climograph for different places across
the globe.

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Griffith Taylor’s Scale of Discomfort was divided into six categories. These are
as follows:

1. 40OF – 45OF represents YHU\UDUHO\XQFRPIRUWDEOH

2. 45OF – 55OF represents LGHDO FRQGLWLRQ

3. 55OF – 60OF represents YHU\UDUHO\XQFRPIRUWDEOH

4. 60OF – 65OF represents VRPHWLPHVXQFRPIRUWDEOH

5. 65OF – 70OF represents RIWHQXQFRPIRUWDEOH

6. 70OF – 75OF represents XVXDOO\XQFRPIRUWDEOH

The location of this twelve sided figure in the graph also gives us the idea
about the climatic condition of that particular place. How is it possible? This is
possible because each corner depicts a particular type of climatic condition.
For example, if the climograph is located in the north western corner of a
graph, it indicates hot and dry conditions. This also indicates that particular
place is situated in arid or semi-arid areas.
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Apart from the position of climograph, the shape of climograph is also helpful
in identifying the nature of climate. Some of the prominent shape and its
associated climate are given below.

(i) A spindle shaped climograph shows dry continental type of climate.

(ii) North East to South West diagonally oriented climograph represents
monsoon type of climate.
(iii) North West to South East diagonally oriented climograph represents
Mediterranean type of climate.
(iv) Climograph which is fully spread represents the British type of Climate.

Let us discuss methods of construction of climograph with the help of an

example given below. You will also be provided with more exercises in the
Practical Manual in integrated laboratory course, BGGCL 134.

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(i) Draw X-axis and Y-axis on a graph sheet as OX and OY respectively.

Mark Relative Humidity (RH), in the X-axis and Wet-Bulb Temperature in
Y-axis. As you have already studied in the Course on Physical
Geography, Wet-Bulb Temperature is either in Degree Celsius or Degree
Fahrenheit (oC or oF), and Relative Humidity is in percentage (%).

(ii) The Wet-Bulb Temperature is plotted in Y-axis, graduated from -10 oF to

90 o F while the relative humidity is plotted along the X-axis graduated
from 20% to 100%. Do you know why this fixed value is taken into
consideration? As mentioned earlier, in this graph, mean monthly values
of Wet-Bulb Temperature are plotted against those of Relative Humidity
on a fixed frame as devised by Taylor to show the physiological effects of
climate on human beings.

(iii) To represent above said two climatic indicators in X-axis and Y-axis, we
have to select a suitable scale. You have already learnt about different
types of scales in Unit 3, Block 1 of this course. In this case, we have
selected a scale of 1 CM = 100 F for Wet Bulb Temperature and 1CM =
200 10 % for Relative Humidity.
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(iv) Once we selected the scale and mark the X-axis and Y-axis accordingly,
try to plot 12 points which represents Relative Humidity and Wet-Bulb
Temperature of 12 months of the year. How to do it? For example, to get
the points for the month of January, you have to draw perpendiculars
from 6.5 cm (64.8/10) and 4.0 (40/10), that represents Relative Humidity
and Wet-Bulb Temperature for the month of January. The point of
intersection of these perpendiculars will show the position of point
representing the values of January month. Mark the letter ‘J’ at this point.

(v) In a similar manner, plot other points representing the remaining eleven
months and mark their names in similar way as suggested in the
previous paragraph. Each month is represented by a letter symbol. In
this case, the symbols are generally represented by first letter of their
names written in capital letters. For example, September would be
represented by the letter ‘S’ whereas October would be represented by
the letter ‘O’ and so on.

(vi) Join all the 12 points sequentially with the help of a scale and complete
the 12 sided polygonal figure. When you will complete the exercise, your
climograph would look like the diagram as given below (see Fig. 12.1).
Write down the words ‘Raw’, ‘Muggy’, ‘Scorching’ and ‘Keen’ in four
corners of the diagram as explained earlier.

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Hythergraph is another form of climatological diagram. This diagram was first
devised by Griffith Taylor. Like climograph, hythergraph also represents
climatic condition of a particular place. Then the question that automatically
might be arising in your mind is that then why another diagram for the same
purpose? As you know, climate of a particular place is determined by various
weather elements like temperature, pressure and precipitation etc. In a two
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dimensional diagram, we cannot plot more than two variables. Therefore,
various climatic diagrams were developed by using combination of any two
suitable variables.

The only difference between climograph and hythergraph is of the indicators. If

you remember correctly, in climograph relative humidity is plotted in X axis
whereas wet bulb temperature is plotted in Y axis. In the case of hythergraph,
rainfall is plotted in X axis whereas temperature is plotted in Y axis. Therefore,
K\WKHUJUDSKis also another twelve sided polygon that represents mean
monthly temperature and rainfall of a particular selected station against one
another. Secondly, unlike climograph, the propounder of this diagram did not
coin any term for representing climatic conditions.

Construction of a hythergraph is similar to climograph. Let us understand the

construction of a hythergraph by solving the below given exercise.

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(i) Draw X-axis and Y-axis on a graph paper as OX and OY respectively.

Mark mean monthly rainfall on the X-axis and mean monthly temperature
on the Y-axis.

(ii) To represent above said two climatic indicators in X-axis and Y-axis, we
have to select a suitable scale. In this case, we have selected a scale of
1 CM = 30 C Temperature and 1CM =10 mm for rainfall.

(iii) Once we selected the scale and mark the X-axis and Y-axis accordingly,
try to plot 12 points which represents mean monthly rainfall and mean
monthly temperature of 12 months of the year. How to do it? For
example, to get the points for the month of January, you have to draw
perpendiculars from 4.7 (14/3), and 2.5 (25/10), that represents the
values of temperature and rainfall for the month of January. The point of
intersection of these perpendiculars will show the position of point
representing the month of January. Mark the letter ‘J’ at this point.

(iv) In a similar manner, plot other points representing the remaining eleven
months and mark their names in similar way as suggested in the
previous paragraph. Each month is represented by a letter symbol. In
this case, the symbols are generally represented by first letter of their
names written in capital letters as you have done in climograph. Join all
the 12 points sequentially with the help of a scale and complete the 12
sided polygonal figure. When you will complete the exercise, your
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hythergraph would look like the diagram as given below (Fig. 12.2).

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Match the two columns.

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A) Spindle i) Monsoon

B) Diagonal (North East-South West) ii) Continental

C) Fully Spread iii) Mediterranean

D) Diagonal (North West-South East) iv) British Type

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The word ergo was derived from Greek word erogon which means work.
There are certain economic activities that are performed during different
periods of the year or in a particular season. Therefore, ergograph depicts
economic activities performed during different seasons of the year along with
area or production. This was developed by Arthur Geddes. This graph also
contains associated weather phenomena that favour a particular type of
economic activities. Till now, you might have realized that this diagram depicts
multiple variables.

Let us explain this with an example. In India, crops are grown in different
seasons and are known as Rabi, Kharif and Zaid. Rabi crops like wheat are
grown in winter months, rice is mainly a kharif crop grown during the hot and
wet seasons and crops like sugarcane requires ten months from sowing to 203
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harvesting. When we prepare ergograph of a particular place, we represent
weather along with the area utilized for growing crops. Mostly two to three
elements of weather we depict are temperature, humidity and rainfall. This is
because these two elements of weather have direct relationship with growing
of crops.
In this diagram, we use combination of three types of statistical diagrams.
Temperature and humidity are represented by line and rainfall is depicted
through bar. The third dimension representing cultivated area is presented in
the form of rectangular diagram.
However, Arthur Geddes and A. G. Oglive prepared circular ergograph to depict
the continuous rhythm of activities performed in different seasons throughout
the year. Here, we will construct an ergograph as suggested in the first case.
Let us understand the processes involved in the construction of ergograph
through an example.
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(i) Draw X-axis and Y-axis on a graph paper as OX and OY. In X-axis, we
represent twelve months and in Y-axis we represent temperature and
rainfall. Area covered under different crops will be shown through
rectangular diagram and placed below the graph. We will discuss it in
detail while discussing about its construction steps.

(ii) To represent above said two climatic indicators in X-axis and Y-axis, we
have to select a suitable scale. In this case, we have selected a scale of
1 cm = 30 C temperature and 1cm = 20 mm for rainfall.

(iii) As temperature is a continuous data, it is represented through line

diagram and rainfall is a discrete data, it is normally represented through
bar diagram. Plot the points for temperature of each month after
converting it according to scale. Once you mark the twelve points for the
204 twelve months, join them with free hand and complete the line diagram.
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Similarly, convert the data related to rainfall according to the scale and
construct twelve bars representing twelve months of a year.

(iv) As mentioned above, area would be represented through rectangular

diagram. The formula for calculating area is as follows:

Area = Length x Breadth

Like temperature and rainfall, we have to fix a scale for area of production. Let
us assume 1 cm = 10,000 hectare.

By doing so, we will get the value for area to be represented in the graph. In
our map, length is already derived. Can you identify how it is derived? It is very
simple. If one month is shown by 1 cm, then six months would be shown by 6
cm, 10 months by 10 cm and so on. Once we obtain the value for area and
length, we can easily calculate the breadth or width of a rectangle
(Breadth=Area/Length).
(i) After obtaining all the values, we will construct rectangular diagram to
represent the area. When you will complete the exercise, your ergograph
would look like the diagram as given below (see Fig. 12.3).

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This diagram is also known as star diagram or direction diagram. It’s because
this diagram looks like a star in which the light emanates from the centre to all
the directions. As you know, there are sixteen directions – four cardinal or
primary directions and twelve secondary directions. Therefore, in a wind rose,
maximum sixteen lines can be drawn from the centre representing
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The length of each line would be proportionate to the quantity it represents. So,
each ray will represent the number of hours or days, the wind blows from the
corresponding direction in a particular period. But there are some hours or
days (as the case may be), when the wind is calm. These calm periods are
generally shown by drawing a small circle at the centre and writing the number
within the circle. After all the lines are drawn, the end points of all the lines are
joined. This closed diagram is known as star diagram.

Like other cases, let us understand the process of constructing wind rose
through the below given exercise.

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1. Draw a small circle having radius of 1 cm. There is no strict rule for it. It
can be little bigger also. The basic purpose of drawing the circle is to
write the number of calm days inside the circle.

2. Draw a horizontal straight line that passes through the centre

representing east-west direction. Similarly, draw a vertical straight line
bisecting horizontal line which would represent north and south direction.
Needless to say, that this vertical line will also pass through the centre.
These two lines will represent four cardinal directions.

3. To find out the rest of four secondary directions i.e., north east, south
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east, north west and south west, bisect all the cardinal directions
associated with it. For example, to derive north east, bisect the area
between north and east at 45 degree angle and draw the straight line.
Derive rest of three secondary directions in a similar manner.

4. To decide the length of all the eight lines drawn, we have to choose a
scale. In this exercise, let us assume 1 cm = 10 days. Accordingly, let us
calculate length to represent wind flow in all directions. For example, the
length for the north direction would be 1.4 cm whereas for east, it would
be 6.4 cm. Calculate for the rest of the six directions accordingly.

5. Once we draw the eight lines according to the scale, join the tip of each
line by drawing straight lines with the help of a scale and complete the
diagram. When you will complete the exercise, your diagram would look
like the diagram as given below (see Fig. 12.5).

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(i) Ergograph was developed for the first time by Griffith Taylor.

(ii) The word ergo was derived from Greek word erogon which means work.

(iii) In a wind rose, maximum twelve lines can be drawn from the centre
representing corresponding four cardinal and eight secondary directions.

(iv) In wind rose diagram, calm period is generally shown by drawing a small
circle at the centre and writing the number within the circle.

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In this unit, you have studied so far:

x Climatic elements namely temperature, pressure, humidity, precipitation

etc. are represented through maps and diagrams. Some of the methods
used for representation of climatic data are wind rose, star diagram,
climograph, hythergraph and ergograph. 207
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x Climograph or climogram is a twelve sided polygon that represents
selected two climatic elements of a particular place against one another.
This twelve sided polygon or climograph was constructed by taking wet
bulb temperature and relative humidity as indicators for representing
climatic condition of a place.

x This was first conceived by Ball in 1910 and later improved by Leighly
(1926), USDA (1941), and Taylor (1949). This diagram was also
extensively used by Koeppen to summarize variations in world climatic
conditions.

x Hythergraph is another form of climatological diagram. This diagram was

first devised by Griffith Taylor. Like climograph, hythergraph also represent
climatic condition of a particular place. Hythergraph is also another twelve
sided polygon that represents mean monthly temperature and rainfall of a
particular station against one another.

x The word ergo was derived from Greek word erogon which means work.
Therefore, ergograph depicts economic activities performed during
different parts of the year along with area or production. This was
developed by Arthur Geddes. Arthur Geddes and Oglive prepared circular
ergograph to depict the continuous rhythm of activities performed in
different seasons throughout the year.

x Wind rose is also known as star diagram or direction diagram. It’s

because this diagram looks like a star in which the light emanates from the
centre to all the directions. Each ray will represent the number of hours or
days, the wind blows from the corresponding direction in a particular
period.

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1. What is a Climograph? Who used climographs scientifically to divide the
world into climatic regions? Describe the ‘Scale of Discomfort’ developed
by Griffith Taylor.

2. Who was the founder of hythergraph? What are the similarities and
dissimilarities between hythergraph and climograph?

3. What is an ergograph? Describe the purpose of an ergograph.

4. What is a wind rose? What is the significance of each “spoke” in the wind
rose? How do we represent calm days in wind rose?

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1. (i) Satellite image, diagrams

(ii) Automated weather station

(i) Effective, easily understandable

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2. A - ii; B - i, C - iv; D - iii

3. (i) False

(ii) True

(iii) False

(iv) True

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1. Your answer should include all the key points like meaning and
terminologies with reference to Climograph systematically as explained in
the Section 12.3.1.

2. In order to answer this question, you should highlight the key differences
between the two by referring to the Section 12.3.2.

3. Your answer should briefly describe the ergograph and highlight its main
purpose. Refer to the Section 12.3.3.

4. Your answer should briefly incorporate the meaning, significance and

highlight the importance of calm days in a wind rose diagram. Refer to the
Section 12.3.4.

 5()(5(1&(668**(67(')857+(5
5($',1*
x Khullar, D.R. (2003), Essentials of Practical Geography. Jalandhar: New
Academic Publishing Co.

x Mishra, R. P. and Ramesh, A. (1989). Fundamentals of Cartography. New

Delhi. Concept Publishing Company.

x Robinson, Arthur, H.J., Morrison, P., Muehrke, A., Kimmerling & Guptill,
S. (eds.) (1995). Elements of Cartography. New York: Wiley.

x Sarkar, A. (2009). Practical Geography: A Systematic Approach. Kolkata.

Orient Blackswan Private Limited.

x Singh, L.R. and Singh, R. (1973). Map Work and Practical Geography.
Allahabad: Central Book Depot.

x Singh R. L. and Singh, R. P. B. (1991). Elements of Practical Geography.

Ludhiana. Kalyani Publishers.

209