A line graph is a way of showing the relationship between two interval- or ratio-level variables. By convention, the independent variable is drawn along the abscissa (x-axis), and the dependent variable on the ordinate (y-axis). The x-axis can be either a continuous variable (e.g., age) or time. It is probably the most widely used type of chart because it is easy to make and the message is readily apparent to the viewer. Line graphs are not as good as tables for displaying actual values of a variable, but they are far superior in showing relationships between variables and changes over time.
The idea of specifying the position of a point using two axes, each reflecting a different attribute, was introduced by Rene Descartes in 1637 (what ...
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