Use the titles of the vertical and horizontal axes of a line graph to understand the plotted points on it. The horizontal axis reflects an independent variable, such as time elapsed or occurrences of an event, while the vertical axis reflects the effect of that variable on a different factor.
One example of a line graph could track the temperature of a particular place over time. The horizontal axis could reflect the time of day, with marks set up every 15 minutes, every hour, every six hours or the time periods at which measurement of the temperature is desired.
Measuring the temperature at the assigned time provides the information for the points on the graph. The marks going up the vertical axis could begin at zero and go several degrees above the highest temperature that the area generally receives at that time of year; if the temperature goes below zero, then the vertical axis range should include negative numbers. At each assigned time, measuring the temperature provides the coordinates for the point. At 8:00 p.m., if the temperature is 55 degrees Fahrenheit, then the right point to plot would sit above 8:00 p.m. on the horizontal axis and at 55 degrees Fahrenheit on the vertical axis. At the next point in time on the horizontal axis, measuring the temperature again provides the next point. Connecting the points with a line completes the line graph.