Plotting Points

 

About

The most important reason for plotting points is to study relationships between variables.

Demonstration

Consider, for example, the fund raising history of a small public radio station. During its first year of operation listener contributions amounted to $70,000.

The table below gives contribution amounts for several years.

Year 1 3 5 8 11 14
Contributions $70,000 $145,000 $190,000 $230,000 $270,000 $290,000

In order to have a useful plot of this data we will need to have different scales on the two axes. The first coordinate of each of the six points will be the year, and we will measure contributions in $10,000 increments, so the first point will be (1,7), the second (3,14.5), etc.

http://dl.uncw.edu/digilib/mathematics/algebra/mat111hb/functions/coordinates/scat.gif

                           Scatter Plot of Contribution Data

From the scatter plot one sees easily that while contributions are rising, they increased more rapidly in the early years. This visual representation of the data makes trends and patterns more obvious than they are from the data table.