Edge Extender

Extend polygon boundaries outward to meet a parent boundary — for example ADM3 sub-national areas that fall short of their ADM0 country edge. Drop a polygon layer; the tool extends each polygon's edges outward via a Voronoi diagram. Internal gaps or overlaps are detected and cleaned automatically before processing.

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.