Box Plot

A box plot is an exploratory data analysis tool that you can use for examining the statistical distribution of any of your numerical datasets.

To create a box plot, choose " Box plot" from the "View" menu or just choose the icon from the visualization toolbar. Then, select the geography and dataset to view. Your output will consist of a graphic representation of the data, as well as information in a "Graph statistics" window that provides values for the key features shown in the plot.

The box plot displays the relationship between key measures that describe your dataset, including the median, the quartiles, maximum and minimum values, and a range of values identified as "outliers".  The median is the black line that bisects the "box" that gives the box plot it's name. The first (lower) and third (upper) quartiles, which are the medians of the lower and upper halves of the data, form the lower and upper bounds of the box. The data for individual locations are shown as grey bars inside the box and grey points outside the box. The "whiskers" on the box, the horizontal bars at the top and bottom, are placed at 1.5 x the interquartile range (see the illustration on the image below). Points outside the whiskers are considered outliers. The vertical line on which the box and whiskers sit is the range of the dataset over all times included in your SpaceStat project.

Like most tools in SpaceStat, the box plot view is linked to other visualization tools.  For example, you may wish to select "outliers" in the upper tail of the distribution of a dataset, and see where those values occur on the map.  Like most views in SpaceStat, the box plot can be animated; use the animation toolbar , or the same options from the animation pull-down menu, to play through your temporal data. You can also time synchronize this plot so that it animates (see below) in conjunction with another view.   

Graph statistics for box plots

The "Graph Statistics" box on the right side of the box plot window provides numeric values for many of the measures that define the box plot.  Note that if you want to find out other information, such as the range of values included within the set of upper or lower outliers, you can click on values within the box plot to select just those points in an outlier region, and then choose the "Selection" option in the "Show statistics for" box within the Graph Statistics window.  When you do this, the new minimum and maximum values (and all other values) will only be calculated from the subset of selected locations.

Note that you can "undock" the Graph Statistics window by clicking on the symbol in the upper right corner, and hide it by clicking on the button. Undocking allows you to move the window around, and later you can dock the window again. If you choose to close the window, you can view it again by clicking on "Graph Statistics" in the Graph pull-down menu.

The animation and graph toolbars

The far left pull-down menu in the box plot window allows you to hide or show the Animation (shown by default) and Graph (hidden by default) toolbars.   Note that if you wish to change the time step size for animations, this option is available from the Animation pull-down menu.  

From the Graph pull-down menu or toolbar, you have the following options:

• Change the window title and the axis label by choosing "Properties".

• Print your box plot (you can also use Ctrl+P)

• Copy a box plot to the clipboard as an image file so that you can use it in other programs.

• Export an animated box plot.

• Turn the Graph Statistics window off or on (click on the entry in the menu, and the window will toggle on or off).

Most of these options are also available from a menu that will appear if you right click within the box plot window.