Line graph is also known as line chart. It is one of the most common graphs which is used almost in every field. Line graph is a graph in which points belonging to an observation are plotted on X-Y plane and every two consecutive points are joined together using a straight line. Line graph is named so, because a line is used to represent the data. An example of line graph is given below: Sales of a particular organization in different years.
Line graph is preferred when rate of change of quantity is observed.
Few examples of the types of data used in line graph are as follows:
- Speed and time
- Sales and expenditure
- Year and production
- Days and number of an article sold
- Months and household expenditure
- States and their population
- City and temperature
- Height and weight
- Age and weight
Parts mentioned above are discussed as follows:
- Horizontal axis or X axis: Line graph has one horizontal axis which is called X axis. It represents independent variables.
- Vertical axis or Y axis: Line graph has one vertical axis which is called Y axis and is exactly perpendicular to X axis. It represents dependent variables.
Origin: The point where X axis and Y axis meet is called origin. In the above figure, O is the origin.
- Labels: Each axis has to be given a label explaining which variable it is representing.
Data Points: In line graph, points are plotted corresponding to X axis and Y axis. These points are called data points. In the above figure, A, B, C and D are data points.
Line segments: Every two data points are joined together by a straight line. In the above figure, AB, BC and CD are line segments.
- Identify independent and dependent variables from the data. This can be done by simply looking at the data and type of variables.
- Choose a scale for independent data and mark it at X-axis.
- Put the label (name of independent variable) for X-axis.
- Choose a scale for dependent data and mark it at Y-axis.
- Put the label (name of dependent variable) for Y-axis.
- Plot the points on the graph.
- Join the points with straight lines.
- Independent variable is "Months" and dependent variable is "Average temperature".
- We chose a scale on X axis: 1 point = 1 month.
- We labeled "Months" on X axis.
- We chose a scale on Y axis: 1 point = 10$^o$C.
- We labeled "Average Temperature" on Y axis.
- We plotted the 12, 18, 25, 35, 40 and 42.
- We have joined them with straight lines.
- Single line graph
- Double line graph
- Multiple line graph
Double Line Graph: This is a graph which contains information about two data sets. It is useful in making comparisons between two sets of data. It has two lines in its graph.
Multiple Line Graph: This is a graph which contains information about more than two data sets. It is useful in making comparisons between multiple sets of data. It has multiple lines in its graph.
By comparing both the lines, we can easily say that overall profit of company A is greater than that of company B and profits of both the companies were equal in year 2004-05.
- Determination of dependent and independent variable.
- Determination of item measured and its unit.
- Determination of rate of change of an item.
- Comparison of two or more data sets in case of double line and multiple line graphs.
- Estimating peaks or ups and valleys or downs.
- Forecasting future results.
|Number of cars sold
- Which month were the highest number of cars sold?
- Which month were the lowest number of cars sold?
- What is the range of cars sold from January to June?
- How many months had sell less than 30?
- The highest number of cars were sold in the month of May and is 45.
- The lowest number of cars were sold in the month of January and is 20.
- The range of cars sold from January to June = 45 - 20 = 25
- January and March months had sell less than 30.
Which days were the maximum and minimum temperature noted in New York?
- Which day were the maximum and minimum temperature noted in San Diago?
- On which day, exactly same temperature was noted in both the cities?
- Maximum temperature was noted in New York on Thursday and Saturday and was 16$^o$C. Minimum temperature was noted in New York on Wednesday and was 13$^o$C.
- Maximum temperature was noted in San Diago on Thursday and was 18$^o$C. Minimum temperature was noted in San Diago on Tuesday and Saturday and was 15$^o$C.
- On Tuesday, exactly same temperature (15$^o$C) was noted in both the cities.