How to create and customise Stiff plots in p:IGI+

P:IGI+ v3.1 and later can generate Stiff plots from sample data to support the visual interpretation of geochemical water analyses. Stiff plots allow users to compare the ionic composition of water samples across a project.

Creating Stiff plots

Step 1. Create a new Stiff plot

Go to Graph à New Graph à New Stiff plot...

2. Search for the required properties in the Search for properties box, then drag them into the Left-axis properties (often cations) or Right-axis properties (often anions) lists.

Note: There must be an equal number of properties in the left-axis properties and right-axis properties boxes. All selected properties must have the same indicator group, unit group and ratio group.

3. Select Create

Note: A Stiff plot is created for the first 100 samples in the project with the selected properties.

Step 2. Edit unit and axes

Right-click à Open graph manager

2. In the Axes tab, select the required indicator, unit and ratio for the x-axis

Note: meq/L is the most commonly used unit for Stiff plots.

3. Select Set axis ranges to start at zero if required.

4. Select Make the right axis the same as left if both axes should use the same range.

5. Set axes ranges by editing the numbers in the boxes next to Left axis range and right axis range.

Customising Stiff plots

Step 1. Edit plot style

1. Right-click à Open graph manager…

2. In the Layout tab, click Plot style… to open additional options and to edit plot layout.

Step 2. Display samples in a grid layout

Select Show each sample on grid
Select the number of panels and columns required

Note: maximum grid size is 10 x 10

3. Choose from fill and line options.

4. Close the Graph manager window.

The Stiff plot layout will automatically update to reflect the selected layout.

Note: If the project contains more samples than the selected grid can display, the grid fills first and the remaining samples are counted in Unshown samples in the Data summary.

Step 3. Add/remove vertical line at zero and/or grid lines

1. Right-click à Open graph manager…

2. Select Horizontal axis grid lines check box to view vertical grid lines on the Stiff plots. Uncheck box to remove.

3. Select Vertical line at zero check box to view central line. Uncheck box to remove.

Step 4. Add data labels

Right-click à Open graph manager…
In the Data labels tab, choose the property from which the data labels will be taken.
Edit the display precision and legend entry text as necessary.
Choose the option to Label the currently brushed points only if required.

The data labels will appear beneath each of the individual samples.

Once created, artefacts can be applied to Stiff plots by dragging and dropping onto the plot window, the same as for any other p:IGI+ graph type.

Note: The order in which the Stiff plots are drawn respects the palette applied.