Fix a Zero-Area Polygon Ring (Degenerate) (WKT and GeoJSON)

A zero-area ring is a ring that technically looks like a polygon, but it encloses no area.
Most validators reject it, and many GIS tools fail or return strange results.

This guide shows a practical way to:

Spot the error quickly.
Decide if it is safe to drop the ring.
Repair it in the editor when dropping is not OK.
Validate the result.
Export clean WKT or GeoJSON.

What “zero area ring” means (in plain terms)

A polygon ring needs at least 3 distinct corners that form a real shape.
If the points are all on the same line, or the shape collapses back on itself, the ring has zero area.

Typical symptoms

Validator errors like Zero area, Degenerate ring, or Area is zero.
A polygon that renders as a line, a spike, or a tiny dot.
Buffer, union, clip, or export steps failing later in a pipeline.

Quick diagnostic. Confirm it is a zero-area ring

Open WKT Validator or GeoJSON Validator.
Paste your geometry.
If you see an error like ring(s) have zero area (degenerate), you are in the right place.

Minimal example. WKT ring with zero area

This ring is closed, but all points are collinear, so it encloses no area.

POLYGON((0 0, 1 0, 2 0, 0 0))

Minimal example. GeoJSON ring with zero area

{
  "type": "Polygon",
  "coordinates": [
    [
      [0, 0],
      [1, 0],
      [2, 0],
      [0, 0]
    ]
  ]
}

Why this happens

Common causes:

A polygon was accidentally exported as a line-like shape.
Simplification removed important corners and collapsed the ring.
Duplicate or near-duplicate points caused a ring to fold into itself.
A hole ring was created by mistake and has no real shape.

Fix it in the browser (ClearSKY Polygon Tools)

Option A. Drop the zero-area ring in the validator

This is the fastest fix when the degenerate ring is not important.

Open WKT Validator or GeoJSON Validator.
Enable Drop zero-area rings.
Copy the fixed output.
Re-run validation on the fixed output.

Important: Dropping rings can remove holes. If the outer ring is zero-area, dropping it can remove the entire polygon part.

Use this option when:

The broken ring is a junk hole, or a tiny artifact.
You prefer a clean geometry over keeping every ring.

Option B. Fix it in the editor by adding or moving vertices

Use this when you must keep the ring, or when dropping it removes something real.

Open /editor and paste or import the geometry.
Zoom to the ring that looks collapsed.
Add a vertex or move a vertex so the ring encloses a real area.
Save and re-run validation.

Rule of thumb: You need at least three non-collinear corners. A triangle that actually has area is enough.

Option C. Delete the bad hole only (common case)

Sometimes the outer ring is fine, but one hole is degenerate.

Open /editor.
Find the hole that renders as a line or spike.
Delete that hole ring, or redraw it properly.
Validate again.

If you need the hole to exist, redraw it. If it is an artifact, delete it.

Special cases you should not miss

A MultiPolygon can contain a degenerate part

If only one part of a MultiPolygon is degenerate, you usually want to remove or rebuild that part, not the whole geometry.

In /editor, split the MultiPolygon into parts, delete or repair the bad part, then export again.

Consecutive duplicates can hide the real problem

If your ring has many repeated points, start with a cleanup pass:

Enable Remove consecutive duplicates.
Then check if the ring still has zero area.

This will not fix a truly degenerate ring, but it can make the geometry easier to repair.

Validate the fixed result (do not skip this)

After any fix:

Re-run validation (WKT or GeoJSON).
Visually confirm the outline looks correct.
Check area and bounds. If values look extreme, you may have a CRS or coordinate issue.

If validation still fails, look for other issues:

Ring not closed.
Too few vertices.
Self-intersections.
Holes outside the outer ring.

If you are using QGIS or PostGIS

QGIS

Useful tools, names may vary by version:

Check validity (to locate the issue)
Fix geometries (attempts repair)
Simplify (be careful, it can create degeneracy)

Always compare before and after. Automatic fixes can drop rings.

PostGIS

Handy functions:

ST_IsValid(geom) to check validity.
ST_IsValidReason(geom) to get the reason.
ST_MakeValid(geom) to attempt repair. It may change the structure.

Example:

SELECT ST_IsValidReason(geom)
FROM my_table
WHERE id = 123;

UPDATE my_table
SET geom = ST_MakeValid(geom)
WHERE id = 123;

If the repaired geometry returns a MultiPolygon and you expected a Polygon, you may need a rule such as keeping the largest part.

Prevention checklist

Avoid over-aggressive simplification.
Validate after any conversion step.
Keep enough coordinate precision during exports.
If you digitize manually, make sure the ring encloses a real area before exporting.

FAQ

›Is a zero-area ring the same as a ring not being closed?

No. A ring can be perfectly closed and still have zero area. Ring closure is about the first and last point matching. Zero area is about the ring failing to enclose any area.

›Should I always drop zero-area rings?

Not always. Dropping is fine for junk rings or accidental hole artifacts. If the ring represents something real, fix it in the editor by adding or moving vertices so it encloses area.

›Why did dropping zero-area rings remove my polygon?

If the outer ring is degenerate, the polygon part has no valid boundary. Dropping it removes that part. In that case, you need to redraw or repair the outer ring in the editor.

›Can simplifying create zero-area rings?

Yes. If simplification removes key corners, a ring can collapse into a line. If you simplify, validate immediately afterwards, and consider using smaller tolerances.

›My ring has area, but the validator still says zero area. Why?

Common causes are extreme rounding, repeated points that collapse segments, or a ring that folds back on itself in a way that cancels area. Try removing consecutive duplicates, then repair the vertices in the editor.