The standard number line was demonstrated in the previous chapter. It can be thought of as a straight line with 0 in the center, positive numbers to the right, and negative numbers to the left. Using these numbers, along with fractions, any point along that line can be expressed as being some distance away from 0, such as 1, −3, or 7½. This is an example of a one-dimensional (1D) coordinate system, or graph. 0 is called the origin because it is the reference point, the starting location, from which any distance along the line is measured.
Figure 3.1: 1D coordinates