Encyclopedia

Learn the history and popular uses for dozens of diagrams, charts, and visuals.

Line Chart

A Line Chart compares two typically numerical aspects of a single object. For example, a marketing department may plot the change in the amount of money the company has over time. The Line Chart consists of an x-axis, which is horizontal, and a y-axis, which is vertical. Most Line Charts only deal with positive number values, so these axes typically intersect near the bottom of the y-axis and the left end of the x-axis. The point at which the axes intersect is always (0, 0). Each axis is labeled with a data type. To carry the example from before, the x-axis would be a unit of time (this could be days, weeks, quarters, years, and so on) and the y-axis would be the amount of money in dollars (or thousands of dollars, and so on). There would be a corresponding set of data. For example, on week 1, the company had ten thousand dollars. Then a point would be plotted over the "Week 1" part of the x-axis and next to the "$10,000" part of the y-axis. After all points are plotted in this same manner, they are connected by a line in a "dot-to-dot" fashion.

The x-axis is also called the independent axis because its values do not depend on anything. For example, time is always placed on the x-axis since it continues to move forward regardless of anything else. The y-axis is also called the dependent axis because its values depend on those of the x-axis: at this time, the company had this much money. The result is that the line of the chart always progresses in a horizontal fashion and each x values only has one y value (the company cannot have two amounts of money at the same time).

More than one line may be plotted in the same axes as a form of comparison. For example, a Line Chart comparing the amount of money held by each department could be created, with a line for each department. In this case each line would have a different color, and a legend would be required.

Line Chart
Typical Uses

As mentioned with the example above, the Line Chart is a powerful visual tool for marketing and other financial areas. It is also used in laboratory research, weather monitoring, or any other function involving a correlation between two numerical values. If two or more lines are on the chart, it can be used as a comparison between them.

Best Practices
  • Determine the purpose. Decide for what purpose the chart is being created. Gather data; it is advisable to place it into a two-column table corresponding to the x- and y-axis. On the top of the page, place a title that briefly describes the purpose of the chart.
  • Create a table. Draw the x- and y-axis on the page. Leave enough room to label them and give them titles, but otherwise fill the page.
  • Label each axis. If time is one of the factors, it should go along the horizontal (x) axis. Whatever other numeric values are being included should be placed along the vertical (y) axis. Each axis should be labeled with the name of the numeric system as well as the measurements being used. For example, an axis title may be "Time (Days)", indicating that each number written on the axis is a number of days. Divide each axis evenly into applicable increments.
  • Create lines. For each item being compared, add a line along the grid. To do this, place a dot at each point that applies to the item and connect each of the dots. If there are multiple lines, each should be in a different color and/or point shape. You may also choose to label the exact value for each point if you want to ensure accuracy.
  • Create a key. Create a key that identifies what each line is by its color.
  • Verify accuracy and share. Consult with coworkers or team members to be sure that the chart is accurate before sharing it with others.

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