GeoJSON Topology Auditor
Check how GeoJSON regions meet or overlap, and locate ring closure, crossing and hole errors by original feature, polygon, ring and edge number. A narrow separation within your tolerance is a gap candidate, not a proven missing coverage region. All calculations run locally without map tiles or an external API.
Key features
- RFC 7946 Polygon and MultiPolygon input with 2D longitude–latitude and an optional ignored third altitude ordinate
- Open, short or zero-area rings, zero-length edges, self-intersections and hole containment/overlap diagnostics
- Separate confirmed interior overlap from an exactly shared boundary
- Candidate gaps between nearby parallel edges and narrow sliver warnings under a degree tolerance
- SVG, CSV and JSON reports containing original feature, part, ring and edge indexes plus coordinates
- Strict JSON parsing and local limits of 120 KB, 32 features and 800 coordinates
How to use
- Paste a Polygon or MultiPolygon GeoJSON object or choose a local file. The example exercises overlap, a possible gap and self-intersection.
- Choose a near-boundary tolerance from 0 to 1 degree. Zero disables near-gap and narrow-polygon warnings.
- Run the audit and distinguish confirmed errors, warnings and shared-boundary information.
- Select an issue to highlight its map marker and use its feature/polygon/ring/edge indexes to edit the source.
- Save the report as local JSON or CSV, or save the diagnostic map as SVG.
Use cases
- Find open rings and self-intersections before publishing region GeoJSON
- Distinguish true overlap from a precise shared administrative boundary
- Review narrow candidate gaps between parallel boundaries and sliver polygons
- Check the parts of a MultiPolygon and placement of interior holes
Frequently asked questions
Does a gap candidate prove an uncovered region?
No. Without an expected outer coverage boundary, complete missing-area coverage cannot be proven. The tool only identifies a vacant point between near-parallel outer edges.
What are the tolerance units?
Decimal degrees of longitude and latitude. The tool does not convert to meters; ground distance varies by latitude. Use it for preliminary checks of small regions, not cadastral or legal boundary decisions.
How do overlap and shared boundary differ?
An overlap requires evidence that the interiors of both regions occupy the same point. If they share a collinear edge but their interiors remain separate, the tool reports shared-boundary information.
Are holes and MultiPolygons included?
Yes. The first ring is the outer boundary and later rings are holes; every MultiPolygon part is checked. Point, LineString and GeometryCollection inputs are rejected explicitly.
Is this exact across the antimeridian and polar regions?
No. It uses planar longitude–latitude calculations, warns about possible antimeridian-spanning edges, and is not a full geodesic or projected topology engine.
Are my files uploaded?
No. The chosen file and coordinates stay in this browser tab. JSON, CSV and SVG files are created locally only when you request a download.
Privacy
GeoJSON coordinates and files are processed only in this browser tab. There are no uploads, external map tiles or automatic persistence.
Comments & questions