NCERT Class 12 Practical Geography Chapter 3 Rules for Drawing Graphs YouTube Lecture Handouts

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NCERT Class 12 Practical Geography Chapter 3: Graphical Representation of Data- Graphs, Thematic Map

NCERT Class 12 Practical Geography Chapter 3

  • Graphs, diagrams, and maps enhance our capabilities to make meaningful comparisons between the phenomena represented, save our time and present a simplified view of the characteristics represented.
  • The transformation of data through visual methods like graphs, diagrams, maps, and charts is called representation of data. Such a form of the presentation of data makes it easy to understand the patterns of population growth, distribution and the density, sex ratio, age – sex composition, occupational structure, etc. within a geographical territory.
  • Picture is equivalent to thousands of words

Rules for Drawing Graphs

  • Select a right method
  • Select a right scale
  • Design
  • Title, Subtitle & Year
  • Legend
  • Direction

Types of Diagrams

  • One-dimensional diagrams, such as line graph, polygraph, bar diagram, histogram, age, sex, pyramid, etc.
  • Two-dimensional diagram, such as pie diagram and rectangular diagram;
  • Three-dimensional diagrams, such as cube and spherical diagrams.

What we will discuss?

  • Line graphs
  • Bar diagrams
  • Pie diagram
  • Wind rose and star diagram
  • Flow Charts
  • Thematic Maps – Dot, Choropleth & Isopleth

Line Graph

Line Graph
YearProfit (in lakhs)
Line Graph

X and Y Axis, round off the data to nearest place

Time series on X and data quantity on Y


Polygraph Year
YearSchool ASchool BSchool C
Polygraph Name of Student

Polygraph is a line graph in which two or more than two variables are shown by an equal number of lines for an immediate comparison, such as the growth rate of different crops like rice, wheat, pulses or the birth rates, death rates and life expectancy or sex ratio in different states or countries. A different line pattern such as straight line (________) , broken line (…) , dotted line (…) or a combination of dotted and broken line (…) or line of different colours may be used to indicate the value of different variables

Simple Bar Diagram

Simple Bar Diagram
Test no.12345678910
Simple Bar Diagram
  • The bar diagrams are drawn through columns of equal width. It is also called a columnar diagram. Following rules should be observed while constructing a bar diagram:
  • The width of all the bars or columns should be similar.
  • All the bars should be placed on equal intervals/distance.
  • Bars may be shaded with colours or patterns to make them distinct and attractive.
  • A simple bar diagram is constructed for an immediate comparison. It is advisable to arrange the given data set in an ascending or descending order and plot the data variables accordingly

Line & Bar Diagram

Line & Bar Diagram
SchoolStudents in 10th ClassTotal Students
School A253880
School B158630
School C196725
School D224788
Line & Bar Diagram

The line and bar graphs as drawn separately may also be combined to depict the data related to some of the closely associated characteristics such as the climatic data of mean monthly temperatures and rainfall

Pie Diagram

Pie Diagram
PartySeats (%)
Party A62
Party B21
Party C11
Pie Diagram

It is drawn to depict the total value of the given attribute using a circle. Dividing the circle into corresponding degrees of angle then represent the sub-sets of the data. Hence, it is also called Divided Circle Diagram.

If data are given in percentage form, the angles are calculated using the given formulae.

Party A

Party C

Party B

Party Others

  • Arrange the data on percentages of Indian exports in an ascending order.
  • Calculate the degrees of angles for showing the given values
  • Select a suitable radius for the circle to be drawn. A radius of 3,4 or 5 cm may be chosen for the given data set.
  • Draw a line from the centre of the circle to the arc as a radius.
  • Measure the angles from the arc of the circle for each category of vehicles in an ascending order clock-wise, starting with smaller angle
  • Starting with bigger angle will lead to accumulation of error leading to the plot of the smaller angle difficult

Flow Map

Flow Map Table
Flow Map Graph
  • Flow chart is a combination of graph and map. It is drawn to show the flow of commodities or people between the places of origin and destination. It is also called Dynamic Map. Transport map, which shows the number of passengers, vehicles, etc. , is the best example of a flow chart. These charts are drawn using lines of proportional width.
  • The number and frequency of the vehicles as per the direction of their movement
  • The number of the passengers and/or the quantity of goods transported
  • A route map depicting the desired transport routes along with the connecting stations.
  • The data pertaining to the flow of goods, services, number of vehicles, etc.
  • Selection of scale to represent passengers
  • Select a scale to represent the number of trains. Here, the maximum number is 50 and the minimum is 6. If we select a scale of 1 cm = 50 trains, a strip of 10 mm and 1.2 mm thick lines will represent the maximum and minimum numbers
  • Some can be done for water flow as well.

Thematic or Distribution Maps

Thematic or Distribution Maps

Use of graphs and diagrams, at times, fails to produce a regional perspective. Variety of maps may also be drawn to understand the patterns of the regional distributions or the characteristics of variations over space. These maps are also known as the distribution maps

Requirements for Making a Thematic Map
  • State/District level data about the selected theme.
  • Outline map of the study area along with administrative boundaries.
  • Physical map of the region. For example, physiographic map for population distribution and relief and drainage map for constructing transportation map.
Rules for Making Thematic Maps
  • The drawing of the thematic maps must be carefully planned. The final map should properly reflect the following components:
    • Name of the area
    • Title of the subject-matter
    • Source of the data and year
    • Indication of symbols, signs, colours, shades, etc.
    • Scale
  • The selection of a suitable method to be used for thematic mapping.

The thematic maps are generally, classified into quantitative and non-quantitative maps. The quantitative maps are drawn to show the variations within the data. For example, maps depicting areas receiving more than 200 cm, 100 to 200 cm, 50 to 100 cm, and less than 50 cm of rainfall are referred as quantitative maps. These maps are also called statistical maps. The non-quantitative maps, on the other hand, depict the non-measurable characteristics in the distribution of given information, such as a map showing high and low rainfall-receiving areas. These maps are also called qualitative maps explained by Dot, Choropleth & Isopleth Maps

Dot Maps

Dot Maps Total Population

The dot maps are drawn to show the distribution of phenomena such as population, cattle, types of crops, etc. The dots of same size as per the chosen scale are marked over the given administrative units to highlight the patterns of distributions.

All dots should be of same size

  • Determine the number of dots in each state using the given scale. For example, number of dots in Maharashtra will be . It may be rounded to 968, as the fraction is more than 0.5.
  • Place the dots in each state as per the determined number in all states.

Choropleth Maps

Choropleth Maps
Choropleth Maps

The Choropleth maps are also drawn to depict the data characteristics as they are related to the administrative units. These maps are used to represent the density of population, literacy/growth rates, sex ratio, etc.

  • Arrange the data in ascending or descending order.
  • Group the data into 5 categories to represent very high, high, medium, low and very low concentrations.
  • The interval between the categories may be identified on the following formulae i.e.. , Range/5 and Range = maximum value – minimum value.
  • Patterns, shades, or colour to be used to depict the chosen categories should be marked in an increasing or decreasing order.

Construct a Choropleth map to represent the literacy rates in India

  • Arrange the data in ascending order as shown above.
  • Identify the range within the data. In the present case, the states recording the lowest and highest literacy rates are Bihar (47 %) and Kerala (90.9 %) , respectively. Hence, the range would be
  • Divide the range by 5 to get categories from very low to very high. . We can convert this value to a round number, i.e.. , 9.0
  • Determine the number of the categories along with the range of each category. Add 9.0 to the lowest value of 47.0 as so on. We will finally get following categories:
    • 47 – 56 Very low (Bihar, Jharkhand, Arunachal Pradesh, Jammu and Kashmir)
    • 56 – 65 Low (Uttar Pradesh)
    • 65 – 74 Medium (Nagaland, Karnataka, Haryana, West Bengal, Sikkim, Gujarat, Punjab, Manipur, Uttarakhand, Tripura, Tamil Nadu)
    • 74 – 83 High (Himachal Pradesh, Maharashtra, Delhi, Goa)
    • 83 – 92 Very high (Mizoram, Kerala)
  • Assign shades/pattern to each category ranging from lower to higher hues

Isopleth Maps

Isopleth Maps
  • Data related to the administrative units are represented using Choropleth maps. However, the variations within the data, in many cases, may also be observed based on natural boundaries. For example, variations in the degrees of slope, temperature, occurrence of rainfall, etc. possess characteristics of the continuity in the data. These geographical facts may be represented by drawing the lines of equal values on a map. All such maps are termed as Isopleth Map. The word Isopleth is derived from Iso meaning equal and pleth means lines. Thus, an imaginary line, which joins the places of equal values, is referred as Isopleth. The more frequently drawn isopleths include
  • Isotherm (equal temperature) , Isobar (equal pressure) , Isohyets (equal rainfall) , Isonephs (equal cloudiness) , Isohels (equal sunshine) , contours (equal heights) , Isobaths (equal depths) , Isohaline (equal salinity) etc.
  • Base line map depicting point location of different places.
  • Appropriate data of temperature, pressure, rainfall, etc. over a definite period.
  • Drawing instrument specially French curve, etc.
Rules to be Observed
  • An equal interval of values is selected.
  • Interval of 5,10, or 20 is supposed to be ideal.
  • The value of Isopleth should be written along the line on either side or in the middle by breaking the line

Interpolation: Interpolation is used to insert the intermediate values between the observed values of at two stations/locations, such as temperature recorded at Chennai and Hyderabad or the spot heights of two points. Generally, drawing of isopleths joining the places of same value is also termed as interpolation.

Method of Interpolation

For interpolation, follow the following steps:

  • Firstly, determine the minimum and maximum values given on the map.
  • Calculate the range of value i.e.. Range = maximum value – minimum value.
  • Based on range determines the interval in a whole number like 5,10, 15, etc. The exact point of drawing an Isopleth is determined by using the following formulae.

Point of Isopleth

The interval is the difference between the actual value on the map and interpolated value. For example, in an Isotherm map of two places show 28 and 33 and you want to draw 30 isotherm, measure the distance between the two points. Suppose, the distance is 1 cm or 10 mm and the difference between 28 and 33 is 5, whereas, 30 is 2 points away from 28 and 3 points behind 33, thus, exact point of 30 will be between those. Thus, isotherm of 30 will be plotted 4 mm away from 28 or 6 mm ahead of 33 .

  • Draw the isopleths of minimum value first; other isopleths may be drawn accordingly