Plotting Metric Data: Line Plots 

Now that we know different types of metric data and operations we can perform with them, we need to know how to plot the metric data. There are many ways to graph and plot data, but for now we are going to focus on line plots.  

Above is a line plot of the data set 1, 3, 4, 4, 6, 7, 7, 8, 8, 12. Each X represents one data point. A data point can be represented by any mark or shape; all that is required for a line plot is a shape or marker and a number line.  

Visualizing Fractions 

A line plot can be a great way to visualize the position and relation of fractions to each other. 

Example: You go outside and measure the lengths of various beetles in your backyard. The beetles’ lengths in centimeters are: 3/4, 2/3, 5/6, 1/2, 5/6, 3/4, 1/4, 3/4, and 7/12. Plot these data on a line plot. 

Solution: Although not completely necessary, you will want to find some sort of common denominator between all of these fractions so that the line of the line plot can be created neatly and evenly and so that you can more easily see the differences between the data points. The highest denominator is 12 in the data point 7/12. All of the other denominators (4, 3, 2, and 6) happen to go into 12. Let’s convert all of the data in terms of twelfths: 9/12, 8/12, 10/12, 6/12, 10/12, 9/12, 3/12, 9/12, and 7/12.  

Reading Line Plots 

Now that you know how to create a line plot, it is important that you know how to take and understand data from a line plot.  

Example: You find various cups filled with water and measure the amount of mL are in each cup. You decide to make a line plot out of your data. Suppose you still have all of the cups and all of the water, and you want to spread the amount of water evenly between every cup. How many mL of water will go in each cup? Use the line plot below. 

Note: This line plot is a bit different than the other ones we have dealt with in that it does not have a slot for every possible point. This is necessary sometimes if the data has a large enough range that it is implausible to create a slot for every possible point in the range. 

Solution: First, we need to take the line plot and convert it into number data. There seems to be one 10 mL cup, three 20 mL cups, two 30 mL cups, one 40 mL cup, and one cup with between 40 and 50 mL of water. We do not have the exact measurement for this cup, but we can estimate the number based on the position on the line. This data point seems to be 46 mL; it’s in the middle but slightly closer to 50 mL than 40 mL. If you did not have 45 mL but you have some point between but not including 40 and 50 mL, that is fine as well.  

Our next step is determining how much water we have total: 

10 + 20 + 20 + 20 + 30 + 30 + 40 + 46 = 216 mL water 

If we have 216 mL water and 8 cups, then in order to find out the amount of water per cup, we need to find 216 ÷ 8. 

27 mL of water would have to be distributed to each cup if all 8 had an equal amount of water in them. 

Key Points