# Numbers '09: About charts

Use a chart when you want to visually represent trends or relationships that may be more difficult to see when data is presented in a table. In Numbers you can choose from a variety of 2D or 3D chart types to present your data, including pie charts, line charts, bar charts, column charts, and area charts, depending on which works best to make the point with your data, or use a mixed chart to overlay two chart types within the same figure. You can also graph your data in a two-dimensional scatter chart, using linear or logarithmic scales.

You may want to create a chart that compares how bird populations have changed in two alpine sampling regions between 2007 and 2010. This data may first be presented in a table with rows for Region 1 and Region 2. The researcher has counted the number of birds in each region each year from 2007 through 2010, thus having 4 data points (or values) for each region.

If you plot this data as a column chart, it shows four sets of two bars, spanning four years.

In this chart, Region 1 and Region 2 are called the data series because the data points (numbers of birds) from each region are represented by a series of columns of the same color, one for each year. Each column for Region 1 is set beside the corresponding column for Region 2, and each side-by-side set of columns is called a data set or category (2007 is a category, 2008 is a category, and so on).

To give a different emphasis to your data, you can transpose the data so that data points are grouped by region rather than by year. In this case, the data points for each year are represented as a series of columns (data series); in this case each series has only two data points and the groups of columns for each region are categories. So this column chart contains two sets of four columns (data points), one category for Region 1 and one data set for Region 2.

Data series are represented differently in different kinds of charts:

- In column charts and bar charts, a data series is represented by a series of columns or bars in the same fill color or texture.
- In a line chart, a data series is represented by a single line.
- In an area chart, a data series is represented by an area shape.
- In a pie chart, only a single data set (the first data point in each series) is represented on the chart (whichever is listed first in the table).
- In a scatter chart, each point on the graph is determined by both an x and a y value. Two columns of values are plotted as x coordinates and y coordinates on a graph representing the data points in a single data series.