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 — include the header row and the columns are matched by name, in any order.
| # | 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.
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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.
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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.