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A line plot organizes measurement data on a number line using X marks. Each X represents one measurement. Line plots help identify the range of measurements and which measurement appears most frequently.
Measure the same type of object (like pencil length) multiple times. Record each measurement on a number line by marking an X. Discuss patterns (cluster, gap, mode) that emerge.
You already know how to measure lengths in inches or centimeters. Now imagine you measure the length of ten pencils and get these results: 5 in, 6 in, 5 in, 7 in, 6 in, 5 in, 6 in, 8 in, 6 in, 5 in. You have ten numbers, but staring at a list does not easily tell you much. A line plot solves this by placing each measurement on a number line, so the data takes on a visual shape.
To build a line plot, draw a number line that covers the range of your measurements — in this case, from 5 to 8. Each time a measurement occurs, place an X above that number. After placing all ten X marks, the column above 6 will be tallest (four pencils were 6 inches), and the column above 8 will be shortest (only one). At a glance, the shape of the X marks tells you where measurements cluster and where there are gaps.
Three key things to read from a line plot: the range (the spread from smallest to largest measurement), the mode (the value with the most X marks — the tallest column), and any gaps or unusual values that stand out. In the pencil example, the mode is 6 inches, the range spans from 5 to 8, and there are no gaps. If only one pencil measured 8 inches while all others were 5–6, that lone X would jump out as unusual.
Line plots are different from bar graphs even though they both use height to show frequency. A line plot uses the actual number line as its base, so every position has a real measurement value — you can see that 6 is between 5 and 7, and that the gap between 7 and 8 is the same size as between 5 and 6. This makes line plots especially natural for measurement data, where the spacing between values matters.