Introduction to Graphs | Class 8 Maths

Graphs are an essential part of mathematics that help visually represent data, making it easier to understand and interpret. In Class 8 Maths, the chapter “Introduction to Graphs” introduces students to the basic concepts and types of graphs. A graph is essentially a visual tool that helps in understanding relationships between different sets of data. This chapter covers various types of graphs, including bar graphs, pie charts, histograms, and line graphs, each serving a specific purpose in data representation.

A graph is a visual representation of data that illustrates the relationship between different variables. It helps in understanding, analyzing, and presenting data in a clear and concise manner. Graphs are used in various fields such as mathematics, science, economics, and social sciences to make data interpretation easier.

Definition of Graphs

A graph is a visual representation of data designed to display relationships between different variables in an easily interpretable format.

Understanding the components of a graph is essential for effectively interpreting and constructing graphs. Here are the primary components:

• Axis
• Origin
• Scale
• Data Points
• Labels

Let’s discuss these components in detail.

Axis

• X-Axis (Horizontal Axis): This is the horizontal line on the graph. It often represents the independent variable.
• Y-Axis (Vertical Axis): This is the vertical line on the graph. It usually represents the dependent variable.

Origin

The point where the x-axis and y-axis intersect is called the origin. It is typically denoted as (0, 0).

Scale

The scale on each axis represents the units of measurement. Proper scaling is crucial to accurately reflect the data.

Data Points

These are the individual points plotted on the graph, representing the values of the variables.

Labels

Each axis should have a label indicating what variable it represents. Labels should also include units of measurement if applicable.

A graph is a mathematical representation of networks. The purpose of the graph is to show mathematical relations in visual form so that it can be easily understood. There are many types of graph:

• Bar Graph
• Pie Graph
• Line Graph
• Histogram

Bar Graph

Bar graph, also known as bar chart which is a visual tool and is used to compare the data among categories. Bar graph may be horizontal or vertical.

e.g. Below is a bar graph which shows pollution level of each city.

Bar graph represents a discrete value on one axis and category on another axis and the motive is to show the relation between two axes.

The bar graph is an easy way to make a comparison between the set of data.

Pie Chart

A pie chart is a circular chart in which each data is represented in a portion of circle. As the chart is divided into wedge-like sectors the total value of pie chart is always 100%.

e.g. The pie chart below is used to represent people’s choice of Laptop’s brands. The circle as a whole here is represented by all the people who took part in the survey. Since it is a whole, the sum of all percentages represented in a pie graph must add up to 100%.

Steps for Creating a Pie Chart:

• Step 1: Decide the topic of your chart.

• Step 2: Having all the information or data and divide it into a number of items, and the value of each item adding together should have a sum equal to 100%.

When comparing parts of a whole, pie-chart is the ideal method.

Line Graph

A line graph is also known as a line chart. It is used to visualize the value of something over time. The line graph has a horizontal x-axis and a vertical y-axis. The point where axes intersect is called origin i.e. (0,0). Each axis having its own data type. For e.g. x-axis could have months, days, weeks and the y-axis may have a growth increase in shares and revenue.

All data value is represented in points and later they connected by line from one to other i.e. in “dot-to-dot” fashion.

e.g.

Histogram

Both histogram and bar graph are similar but there is a difference between the two that histogram is used to collect numbers into a particular range of number. The histogram is defined as the chart that is used to represent the continuous data.

e.g. Consider the case of the data given below in the table that shows the data obtained in a class test of 35 students as:

Marks obtained	40-50	50-60	60-70	70-80	80-90	90-100
Number of Students	7	3	4	6	5	10

The histogram drawn for this case is drawn as:

Each graph is different from the others, so we cannot describe the process with the same steps. However, some steps are common for most graphs. These steps are:

Step 1: Collect the data you want to represent on the graph.

Step 2: Decide whether you need a bar graph, line graph, pie chart, histogram, etc., based on the data type.

Step 3: Draw two perpendicular lines on your graph paper or plotting software. Label the horizontal line as the x-axis and the vertical line as the y-axis.

Step 4: Mark the axes with the variables they represent (e.g., time on the x-axis, temperature on the y-axis) and choose the appropriate scale.

Step 5: Locate each data point by using the values from your data set. Find the corresponding position on the x-axis and y-axis and place a dot at the intersection.

Step 6: For a line graph, connect the data points with lines. For a bar graph, draw bars from each data point to the x-axis. For a pie chart, draw slices proportional to the data values.

In conclusion, understanding graphs is a fundamental skill in mathematics that helps visualize data, relationships, and patterns. For Class 8 students, this introduction provides a solid foundation in various types of graphs, including bar graphs, line graphs, and pie charts.

What is a graph in mathematics?

A graph is a visual representation of data that shows relationships between different sets of information.

What are the different types of graphs?

There are several types of graphs commonly used in mathematics, including:

• Bar Graphs: Represent data with rectangular bars.
• Line Graphs: Show data points connected by straight lines.
• Pie Charts: Display data as a circular chart divided into slices.
• Histograms: Similar to bar graphs but used for continuous data.

Why are graphs important?

Graphs are important because they provide a visual way to present data, making it easier to identify patterns, trends, and relationships.

How do you choose the right type of graph for your data?

Choosing the right type of graph depends on the nature of your data and what you want to illustrate. For example:

• Use a bar graph to compare different categories.
• Use a line graph to show trends over time.
• Use a pie chart to show proportions of a whole.

Can graphs be misleading?

Yes, graphs can be misleading if they are not created or interpreted correctly. Common issues include using inappropriate scales, omitting data, or choosing the wrong type of graph for the data.