Edge Matcher

Edge Extender + clip — fully in your browser.

Fix gaps and overlaps where adjacent polygon boundaries don't line up — for example ADM3 sub-national areas that don't match their ADM0 country edge. Drop a polygon layer; the tool extends each polygon's edges outward via a Voronoi diagram so they meet cleanly.

Step 1 — Extend boundaries

Drop a file here

or browse

Polygon layer in WGS84 — admin boundaries, basins, etc. GeoJSON · GeoParquet · GeoPackage · Shapefile (ZIP).

Advanced settings

Point spacing along boundary

Default 0.0002° (~22 m) handles country-scale data. Increase to ~0.002° for world-scale; decrease to ~0.00002° for neighbourhood-scale.

Step 2 — Clip to a known boundary (optional)

Trim the extended result to a boundary you trust (e.g. an official ADM0) to remove ocean overshoot.

Finish Step 1 first

or browse

Single polygon (or polygons) to clip the extended result to.

Your files never leave your device.