Objective:

Bar graphs or bar diagrams are helpful in representing the data visually. Here we learn about ,

 

• Definition of Bar Graph
• Parts of a Bar Graph
• Interpretation of a bar graph
• Drawing a bar graph

 

Bar Graph

Representing data by pictograph is not only time consuming but at times difficult too. Let us see some other way of representing data visually. Bars of uniform width can be drawn horizontally or vertically with equal spacing between them and then the length of each bar represents the given number. Such method of representing data is called a bar diagram or a bar graph.

Bar graphs or bar diagrams are helpful in representing the data visually. The length of each bar represents the required information. Choosing an appropriate scale for a bar graph is important. Scale means the number used to represent one unit length of a bar.

For example, the scale for the bar graph shown here is 1 unit length = 100 children.

Parts of a Bar Graph

 

The basic parts of a bar graph are vertically identical to those of a line graph except that the data values of bar graph shown by bars rather than lines and point symbols.

Various parts of the line graph:

 

Title: The title is explains what the graph is about.

 

Scale: The scale is the numbers that show the units used on the bar graph.

 

Labels: Both the side and the bottom of the bar graph have a label that tells what kind of data is shown. X-axis describes what each data point on the line represents and y-axis shows the numeric value for each point on the line.

 

Bars: The bar is measures the data number.

 

Key: Explains any additional information included in the graph. Many times, this will show different colours or symbols used to represent different categories. It is needed only when data about more than one category are shown in graph.

 

Data values: Data values are the actual numbers for each data point.

Interpretation of a Bar Graph

By observing a bar graph we can understand what kind of data it represents and draw certain conclusions from it. This is known as “Interpretation of the bar graph “.

The given Bar graph expresses the following information:

 

 

• It is clear from the bar graph that the bar of minimum height corresponds to the sale on Friday.
Therefore, the sale was minimum on Friday.

 

• From the bar graph, we find that the bar of maximum height corresponds to the sale on Monday.
Therefore, the sale was maximum on Monday.

 

• The total sale during the week = (225 + 100 + 150 + 200 + 75 + 100) bulbs = 850 bulbs.

 

• The minimum sale during the week = 75 bulbs.
The maximum sale during the week = 225 bulbs.

 

• Therefore, minimum sale: maximum sale = 75: 225 = 1: 3.

 

Drawing a Bar Graph

 

Step 1: On a graph paper, draw a horizontal line OX and a vertical line OY. These lines are the x-axis and the y-axis respectively.

 

Step 2: Mark points at equal intervals along the x-axis. Below these points write the names the data items whose values are to be plotted.

 

Step 3: Choose a suitable scale. On that scale determine the heights of the bars for the given values.

 

Step 4: Mark off these heights parallel to the y-axis from the points taken in Step 2.

 

Step 5: On the x-axis, draw bars of equal width for the heights marked in Step 4. They should be centered on the points marked on the x-axis. These bars represent the numerical data.

Let us draw a bar graph for this data

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First of all draw a horizontal line and a vertical line. On the horizontal line we will draw bars representing each fruit and on vertical line we will write numerals representing number of students. Let us choose a scale. It means we first decide how many students will be represented by unit length of a bar. Here, we take 1 unit length to represent 1 student only. We get a bar graph as shown in figure.

 

Summary

 

• We have discussed how to represent data by using a bar diagram or a bar graph.
• In a bar graph, bars of uniform width are drawn horizontally or vertically with equal spacing between them.
• The length of each bar gives the required information.
• To do this we also discussed the process of choosing a scale for the graph.
• For example, 1 unit = 100 students. We have also practised reading a given bar graph.
• We have seen how interpretations from the same can be made.