How to Read a Stereonet — A Beginner's Guide with Examples

1. What a Stereonet Actually Shows

A stereonet — short for stereographic net — is a way to draw three-dimensional orientations on a flat, two-dimensional circle. In structural geology it answers a practical question: which way do my planes and lines point, and do they share a pattern?

Imagine your outcrop at the center of a hollow lower hemisphere, like the bottom half of a globe. A plane (say, a bedding surface) passes through the center and intersects that hemisphere along a curved line. A linear feature (a fold axis, a lineation) pierces the hemisphere at a single point. The stereonet is simply the flattened, bird's-eye view of that hemisphere, with north at the top.

Because every measurement becomes a point or a curve on the same circle, patterns that are invisible in a notebook of numbers jump out visually — that's the whole point.

2. Equal-Area vs Equal-Angle

There are two common nets, and picking the right one matters:

• •Equal-area (Schmidt) net. Preserves the density of points. If you plot 200 measurements, clusters look genuinely denser where data is concentrated. This is the net for statistical work — contouring, finding maxima, analyzing populations. Most field data goes here.
• •Equal-angle (Wulff) net. Preserves angles, which makes it the right choice for precise geometric constructions — rotating data, finding the angle between two planes, working with crystallography.

For everyday field structural analysis — the kind GeoKit's stereonet plotter and the in-app analysis use — the lower-hemisphere equal-area net is standard.

3. Poles vs Great Circles

Every plane can be drawn two ways, and knowing when to use each is the key skill:

• •Great circle. The curved arc where the plane cuts the hemisphere. A gently dipping plane plots as a broad arc near the edge; a vertical plane plots as a straight line through the center. Great circles are intuitive for one or a few planes.
• •Pole. A single point representing the line perpendicular to the plane. One plane = one dot. A steeply dipping plane has a pole near the edge; a horizontal plane has a pole at the center.

The rule of thumb: use great circles for a handful of planes, use poles for many. Twenty great circles overlap into spaghetti; twenty poles form a clear cluster you can actually interpret.

4. How to Plot a Plane

To plot a plane you need its strike and dip. Here's the pole method, step by step:

1. Find the dip direction (90° clockwise from strike, if you're using the right-hand rule).
2. The pole plots on the opposite side of the net from the dip direction — a plane dipping southeast has a pole in the northwest.
3. Its distance from the center depends on dip: a steep plane (dip near 90°) has a pole near the edge; a shallow plane (dip near 0°) has a pole near the center.

You don't have to do this by hand. Enter the numbers into the online plotter and it places the pole (or draws the great circle) instantly — the same equal-area math GeoKit uses in the field.

5. Reading Patterns: Clusters, Girdles & Folds

Once your data is plotted, the pattern tells the story:

• •A tight cluster of poles means the planes are consistently oriented — flat-lying bedding, or a single well-defined joint set. The cluster's position tells you the average orientation.
• •A girdle — poles spread out along a great-circle path — usually means folding. As bedding wraps around a fold, its poles trace an arc. The pole to that girdle (the β axis) gives you the fold axis orientation.
• •Two or more separate clusters point to multiple sets — for example conjugate fractures, or bedding plus a cleavage.

A rose diagram complements the stereonet by summarizing just the strike directions as petals — great for a quick read on the dominant structural trend across a whole area.

6. A Worked Example

Say you measured a set of bedding planes all striking roughly northeast (around 045°) and dipping about 35° to the southeast. Plotted as poles, they form a tight cluster in the northwest quadrant, partway between the center and the edge (because the dip is moderate, not steep). That single cluster says: consistent, moderately SE-dipping bedding — no folding here.

Now add a couple of faults striking around 125°. Their poles land in a different part of the net entirely, telling you the faults cut across the bedding trend rather than following it.

Want to see it? Open the stereonet plotter and hit Load example — it plots exactly this dataset so you can toggle between poles and great circles and watch the pattern.

7. Common Mistakes

• ✕Confusing dip direction with strike. Entering one for the other rotates every point 90°. Be clear which convention your data uses — GeoKit lets you switch between dip-direction, right-hand-rule, and quadrant so there's no ambiguity.
• ✕Mixing up poles and great circles. A pole near the edge is a steep plane; a great circle near the edge is a shallow plane. They're opposites.
• ✕Reading an equal-angle net as equal-area. Density only means something on an equal-area net. Know which one you're looking at before you talk about "clusters."

8. Try It Yourself

The fastest way to understand stereonets is to plot your own data and watch the pattern change. Two free ways to do it:

• →On the web: the GeoKit stereonet plotter — enter or paste strike/dip and plot poles, great circles, and a rose diagram instantly.
• →In the field: GeoKit's in-app structural analysis builds the stereonet, rose, and dip histogram from measurements you take with your phone — automatically, and offline.