Data Interpretation | Line Chart Basics

The line graph or X-Y chart is represented on the X-Y plane denoting trends and changing rates. Basically line charts are the best suited charts for representation of data related to time series and frequency distribution. Take a look at this chart from Microsoft as an example, which shows monthly trends in transactions. 

Line charts are essentially drawn out from bar graphs. If you join the upper points of the bar graph and join them, you will get a line chart only that gives us the above mentioned diagram.

Parts of a line chart or line graph

A line graph encompasses a vertical axis and a horizontal axis. 

• Title – shows what the graph is depicting such as company sales of the year 2018, GDP of 2018-19, etc. 
• Labels – depict what the horizontal and vertical axis are telling us. (E.g. Units sold and Total Transactions)
• Scales – the scales denote the number or quantity of facts and data of the horizontal and vertical scales. 
• Points – represent data on the graph through dots 
• Lines – points are connected to form a line that represent the trend of the data (e.g., are the transactions increasing? Or Decreasing?)

Types of questions asked through a line chart

Any data that is measured against time uses a line chart. Some examples include:

• Population of a country
• GDP or national product 
• Sales or profit making of a company

The questions which can be asked from this section could be of the following type:

1. What is the trend in change of variable?
2. What is the percentage increase or decrease in between two points of time?
3. When was the variable parameter highest/lowest?
4. How the does the total sales of Q1 compare to total sales of Q2? 

Some important properties of a line chart

• You can easily detect the changing trends of the data represented by looking at the graph. 
• While looking at the graph, specific values of the variables and how one variable is affected by another is easily seen. 
• Line graphs are predominantly used for comparing datasets and your questions can be based on such comparisons. 
• Slope of the graph indicates the absolute growth of the data. It does not indicate the percentage of growth. 
• If the slope is steeper, the magnitude change is greater between those two points. 

Some important types of line charts 

• Single variable graph 

This graph shows the changes in a single variable over a certain period of time. For example, sales of a company over 2015-2020. 

• Continuous variable graph

For this two or more lines depict two or more dependent variables. 

• Two scaled graph

If two variables have different units of measurements, two scales are used on the graph. 

Points to keep in mind while solving line chart questions

• While looking at the line chart, pay attention to the details like the trends, data values, and analyse them carefully. 
• Do not assume any information according to your own understanding, read the questions and refer only to the data given in the line chart. 
• Most of the questions will be based on finding out averages, percentages, ratio and proportion, etc. So the formulas of all these should be on your tips. 

Some important formulas

• Average = Sum of all values 

                   Number of values 

• Percentages change = Final value – Initial value   x 100 

                                                     Initial value                     

• Ratio = Comparison of like terms 

Apart from these, pay attention to the basics of mathematical aptitude while practicing questions and you will do wellt in solving line chart questions.