Imagine if you wanted to know how many students in your class have birthdays in each month. First you would ask each student to write down her birthday on a piece of paper. Then draw a horizontal line with numbers 1 through 12, one number for each month. Make a check mark above each month for each birthday in that month. Months with more birthdays will have more check marks, and months with fewer birthdays will have fewer check marks. This line plot shows the distribution of birthdays over the 12 months.
Maybe you wanted to know the distribution of test scores in your class. First, ask each student to write his test score on a piece of paper. Then draw a line with each possible score from 0 to 100. Simply make a check mark above each number when a student received that score. When viewed from a distance, the line plot will show the distribution of scores in the class. If the class did well, there will be more check marks near the right of the line plot, and if the class did poorly, the left part of the plot will be cluttered with check marks.
It is also possible to draw a line plot for heights among a certain group of people, for example a family. Draw a horizontal line labeled from 150 to 200. Then, measure each member of your family (in centimeters) and place their height on the chart. This is a line plot for charts.
Line plots can also help when choosing between various products. For example, if you wanted to only eat low-calorie cereal, you could make a line plot with calories along the x-axis and the name of each cereal as a check mark in the y direction. The cereals with low calories will appear to the left of the line plot, and you could choose your favorite from them.
These four examples should explain how a line plot works. A line plot simply shows the frequency of a certain number (it could be a birthday, height or a score on an exam) in a certain population (in these examples, your classroom). The check marks represent frequency, and the numbers on the line signify the characteristic you want to measure. In some cases, line plots can be useful for choosing between products with different characteristics.