A line plot displays measurement data along a number line, with an X (or dot) placed above a value each time it appears in the data set. To create a line plot from measurements: measure each object, record the measurements, draw a number line spanning the range, and plot one X per measurement. Line plots make it easy to see the most common measurement (the tallest stack of X's) and the spread of the data.
Have students measure several similar objects (pencils, crayons, leaf lengths) in whole inches, then create a line plot from their own data. Ask interpretation questions: 'What length was most common? What was the difference between the shortest and longest?'
You already know two things that come together here: how to read a line plot, and how to measure lengths with a ruler. A line plot with measurement data simply uses the number line to show all the measurements you collected, so you can see patterns at a glance.
Here is how the two skills connect. Suppose you measure the length of 10 crayons to the nearest inch and get these values: 4, 5, 4, 6, 5, 4, 5, 6, 4, 5. You now have a list of numbers — but a list is hard to interpret. A line plot turns that list into a picture. Draw a number line from 4 to 6 (your smallest to largest measurement), then go through your list and place one X above the matching number for each measurement. When you're done, you can immediately see that 4 inches and 5 inches were the most common crayon lengths because those columns of X's are tallest.
The number line must have a consistent scale — equally spaced intervals that match your unit of measurement. If you measured in whole inches, each tick mark is one inch apart. Label the axis with the unit ("length in inches") so anyone reading the plot knows what the numbers mean. Each X represents exactly one object you measured, not a count — this is the most common confusion. If three crayons were 5 inches long, there are three X's above the 5, not the number 3.
Once your line plot is built, you can answer questions about the data directly from the picture. The tallest stack of X's shows the most common measurement (the mode). The distance from the leftmost X to the rightmost X shows the spread — how much variation there is in your measurements. Line plots make data visible, which is exactly what a good display is supposed to do.