Stiff Diagram Generator
Generate Stiff diagrams — one polygon per water sample — to compare hydrochemistry at a glance and post the shapes onto a map.
What a Stiff diagram shows
A Stiff diagram is a polygon built from parallel horizontal axes. Cations are plotted to the left of a central vertical zero line — sodium plus potassium on top, then calcium, then magnesium — and the corresponding anions to the right: chloride, bicarbonate, sulphate. Joining the points produces a closed shape in milliequivalents per litre.
It gives up the classification precision of a Piper plot and gains something a Piper plot cannot do: it keeps absolute concentration. The overall width of the polygon is proportional to total ionic strength, so a dilute and a saline water of identical composition look obviously different — where on a Piper diagram they would plot on top of one another.
Data
Paste straight from Excel or Google Sheets, or import a CSV or .xlsx file — columns are matched by name, in any order, and a workbook can bring one specimen per sheet.
| # | Sample(opt) | Group(opt) | Camg/L | Mgmg/L | Namg/L | Kmg/L(opt) | Clmg/L | SO4mg/L | HCO3mg/L | CO3mg/L(opt) | TDSmg/L(opt) | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | ||||||||||||
| 2 | ||||||||||||
| 3 | ||||||||||||
| 4 |
0 rows of data
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Enter data on the left to plot it
SVG is vector — resize it in Illustrator or Inkscape without losing quality. PNG 4× is roughly 600 dpi at figure width.
Free downloads carry a small “made with strataplot.com” credit along the bottom edge. The plot on screen is never watermarked. Remove it
Export Piper + Stiff + Schoeller
Renders all three hydrochemical diagrams from the table above and downloads them as one zip.
Options
This plot has no adjustable options yet.
Your data is processed entirely in this browser tab. Nothing is uploaded to a server, so confidential client data stays confidential.
How to read it
Read the shape as a fingerprint rather than a measurement. A polygon stretched wide at the top is a Na–Cl water. One bulging at the bottom-left with a matching bulge to the right of the bicarbonate axis is a Ca–HCO₃ water. Two samples with the same shape but different sizes are the same water at different concentrations — dilution by recharge, or concentration by evaporation.
The real strength is spatial. Drop one polygon beside each sample point on a base map and the hydrochemical evolution along a flow path becomes something you can see rather than infer: shapes changing systematically downgradient, a saline wedge growing towards the coast, or a contaminant plume standing out as a family of polygons that do not match the background.
Who uses one
Hydrogeologists and environmental consultants presenting monitoring-well networks, contaminated-land specialists delineating plumes, and coastal groundwater studies tracking saline intrusion.
Common questions
- Why are sodium and potassium combined?
- Potassium is usually a minor constituent in natural groundwater and behaves similarly on this plot, so the conventional Stiff layout combines them onto one axis. Keeping them separate would add an axis for very little information.
- Can I compare Stiff diagrams between figures?
- Only if they share a scale. Because the axes are in absolute meq/L, a polygon is meaningless without its scale bar — always plot a set of samples on a common axis range.
Methodology
A methods paragraph to put beside the exported figure. It describes the tool’s default settings, so edit a clause if you changed one. References are given as the tool’s source code records them.
Major-ion concentrations were converted from mg/L to meq/L with the equivalent weights tabulated by Hem (1985) and Freeze & Cherry (1979), with values below the reporting limit taken as half that limit (Helsel, 2005). Each analysis was drawn as a Stiff (1951) polygon with cations to the left and anions to the right of a zero axis — Na + K against Cl, Ca against HCO₃ + CO₃, Mg against SO₄ — and all polygons share one meq/L scale so that their widths can be compared.
References
- Freeze, R.A. & Cherry, J.A. (1979). Groundwater.
- Helsel, 2005.
- Hem, J.D. (1985). Study and Interpretation of the Chemical Characteristics of Natural Water. USGS Water-Supply Paper 2254.
- Stiff (1951)
- StrataPlot. (2026). StrataPlot: Stiff Diagram [Computer software]. https://www.strataplot.com/stiff-diagram
How to cite this tool
If a figure made here goes into a report, thesis or paper, cite the tool so readers know how it was drawn. Add the date you accessed it if your style guide asks for one.
StrataPlot. (2026). StrataPlot: Stiff Diagram [Computer software]. https://www.strataplot.com/stiff-diagram
@misc{strataplot_stiffdiagram,
author = {{StrataPlot}},
title = {StrataPlot: Stiff Diagram},
year = {2026},
howpublished = {\url{https://www.strataplot.com/stiff-diagram}},
note = {Computer software}
}