Line Graphs
Parts of a Line Graph
In grade 9, we will be working a lot with line graphs so in this lessons we will review the main components. A line graph has two axes usually labeled as \(x\) and \(y\). The values of one variable appear on the horizontal axis (called the independent variable, typically \(x\)), and the values of the other variable appear on the vertical axis (called the dependent variable, typically \(y\)).
To plot a line graph, we will sometimes start by plotting a few individual points and the connect them with a straight line. When you have a graph with just the points, it is called a scatter plot. Points on the graph are indicated by writing their \(x\) and \(y\)-coordinates as a pair like \( (2, 30) \). This point is at \(x=2\) along the \(x\)-axis and \(y=30\) along the \(y\)-axis. Plot a couple points, then draw a line through them to make a line plot. The intersection of the axes is usally labelled as point \((0,0)\) called the origin.
The axes have ticks to indicate quantities along their lines. Positive numbers are located at the right/top and negative numbers are located the left/bottom. The ticks on the axis should be equally spaced, but each tick can represent a different value on different axis. For example, if you are measuring earnings made at your job for every hour worked, the 'number of hours' axis might count by \(1\) but the 'earnings' axis might count by \(10\). Consider the range (minimum and maximum) values along each axis and then make sure your graph covers all those points.
It is also good practice to label your axes with the variable and description. Describe the variable and include the units! Give your plot a title as well such as "Earngs vs Hours worked".
In the graph below, the axes are extended in the negative direction as an example. However, in this case, we would not expect a negative amount of hours worked or earnings:
