A line graph provides several benefits compared to other data representation methods such as a bar or pie chart. There are three characteristics which make it common in many types of work, including heavy usage in scientific endeavors or longitudinal studies.
One of the most important benefits is the longitudinal aptitude of a line graph. The timeline for a tracked event can easily be plotted along an x/y axis. This shows a graphic representation of the rise or fall of data points. Missing data can be plotted along the line with some degree of certainty or error probability. This is also seen with graph convergence, which is most often seen in economic data points. For example, the cost a consumer is willing to pay for an item can be crossed with a profitable sell point for the company to reach the ideal market price.
Another benefit of the line graph is the comparison factor as mentioned briefly above. Two or more items can be compared to cross points, which allows for at the minimum anecdotal evidence of a connection. It should be noted not all line graphs will have the same starting point on a linear graph representing a longitudinal study. The creation of a start point along the axis can demonstrate the continuation or inclusion of different data in time.
The final benefit, as odd as it sounds, is the universal color reproduction of the line graph. Line graphs allow for many more ways to represent the data points. A bar graph can use color to differ between compared items, but colors do not always translate across different print mediums. However, line graphs can use color or different line styles such as dots or dashes. While it seems like a simple item, this advantage allows line graphs to better transfer to black/white paper print.