12th Standard Geography — Representation of Geographical Data Online Test
Unit 12 of 12th Geography, a practical lesson, explains how geographical data are shown as statistical diagrams. It classifies diagrams as one, two and three dimensional, and shows step by step how to draw a simple line graph, a polygraph, simple and multiple bar diagrams and a pie diagram with worked examples.
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About Representation of Geographical Data
Easy ~40 min study
Representation of Geographical Data is Unit 12 of the Tamil Nadu State Board Class 12 Geography book and part of its Practical Geography section. It begins with a simple idea: climatic, population and economic data are easier to understand when they are drawn as graphs, diagrams, charts and maps instead of being left in tables.
The lesson defines statistics and statistical diagrams, lists their three purposes and sorts them into one, two and three dimensional types. It then works through five solved examples: a simple line graph of India's literacy rate, a polygraph of urban population, a simple bar diagram of rice production, a multiple bar diagram of India's population and a pie diagram of the area under wheat.
This page gathers one mark questions on these concepts, the construction steps, the kinds of diagrams and the pie diagram formula, each with a short explanation drawn from the lesson. The printed exercise asks only for drawings, so all questions here are additional.
What you'll learn
- Define statistics and statistical diagrams and state their three purposes.
- Classify statistical diagrams into one, two and three dimensional types with examples.
- List and follow the five steps of constructing a line graph.
- Distinguish a simple line graph from a polygraph.
- Name the four kinds of bar diagram and draw simple and multiple bar diagrams.
- Convert component values into degrees and draw a pie diagram.
Before you start
- Plotting points on graph paper using an x-axis and a y-axis.
- Working out percentages and simple proportions.
- The idea that a circle measures 360 degrees at its centre.
Topics covered in this chapter
Representation of Geographical Data explained
What this lesson covers
Statistics and statistical diagrams
Numerical data collected in a systematic manner and presented in a tabulated form are called statistics. Diagrams that represent statistical data use bars, rectangles, squares, circles, cubes, spheres, curves or lines. They help us compare figures at a glance, leave a memorable impression and draw inferences easily.
Classification
One-dimensional diagrams include the line graph, polygraph, bar diagram and histogram. Two-dimensional or area diagrams include squares, rectangles, circles and pie diagrams. Three-dimensional or volume diagrams include cubes, block piles and spherical diagrams.
Line graphs
Line graphs show time series data such as temperature, rainfall, population, birth rate and death rate. A simple line graph shows one variable; a polygraph shows two or more variables with different line patterns or colours.
Bar diagrams
Bars of equal width, placed at equal intervals, have lengths proportional to the quantities. The four kinds are simple, multiple, compound and percentage bar diagrams; the lesson draws simple and multiple bars.
Pie diagram
A circle of 360 degrees is divided into sectors. Each angle is found as value of component divided by total value, multiplied by 360.
Common mistakes to avoid
- Making bars of different widths. Only the length of a bar shows the quantity; all bars must have similar width.
- Leaving unequal gaps between bars. Bars must be placed at intervals of equal distance.
- Multiplying by 100 instead of 360 when finding pie angles. Angle = value of component / total value x 360.
- Calling a pie diagram one-dimensional. Divided circles are two-dimensional area diagrams.
- Forgetting the title, labels and scale of the axes in a line graph.
Test yourself on these with the practice test, then check the worked reasoning in the solved MCQs.
Frequently asked questions
Why do geographers use statistical diagrams?
Climatic, population and socio-economic data are easier to understand when shown visually. Statistical diagrams let us compare figures at a glance, leave an easily memorable impression on the mind, and help us analyse the data and draw inferences easily, which tables alone do not do.
What are the three classes of statistical diagrams?
One-dimensional diagrams such as line graph, polygraph, bar diagram and histogram show quantities by lengths. Two-dimensional or area diagrams use squares, rectangles and circles, including pie diagrams. Three-dimensional or volume diagrams include cubes, block piles and spherical diagrams.
How is a line graph constructed?
Draw a horizontal x-axis and a vertical y-axis; their meeting point is the starting point, normally zero. Add labels and scales to both axes, plot the data points, draw a line through the plotted points and finally add a title.
What is the difference between a simple line graph and a polygraph?
A simple line graph shows the successive changes in one variable over a period of time, such as India's literacy rate. A polygraph shows two or more variables by an equal number of lines, using different line patterns or colours, for immediate comparison.
What are the rules for drawing a bar diagram?
The length of each bar is proportional to the quantity it represents. All bars should have similar width, be placed at intervals of equal distance, and may be shaded with colours or patterns. Bars may be vertical or horizontal, and data are best arranged in ascending or descending order.
How is the angle of a sector in a pie diagram calculated?
Each component is converted into degrees using angle value = value of component divided by total value, multiplied by 360. For example, Asia's 46.85% of the area under wheat gives 168.66 degrees, drawn as about 169 degrees.
Last updated 19 October 2026