A line graph, also known as a line chart, is a type of chart used to visualize the value of something over time. For example, a finance department may plot the change in the amount of cash the company has on hand over time.
The line graph consists of a horizontal x-axis and a vertical y-axis. Most line graphs 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. For example, the x-axis could be days, weeks, quarters, or years, while the y-axis shows revenue in dollars.
Data points are plotted and 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 graph always progresses in a horizontal fashion and each x value 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 axis as a form of comparison. For example, you could create a line graph comparing the amount of money held by each branch office with a separate line for each office. In this case each line would have a different color, identified in a legend.
The line graph is a powerful visual tool for marketing, finance, and other areas. It is also useful 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.
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