The GeoJSON Geometry Simplifier reduces the number of vertices in polygons and lines so that maps render faster and files transfer smaller, while keeping the geometry recognisable. It uses the Visvalingam-Whyatt algorithm, which is well suited to cartographic simplification because it preserves the visual character of a shape better than distance-based methods. Everything runs in the browser, so even large or sensitive datasets stay local.
How it works
Visvalingam-Whyatt assigns every interior point an effective area: the area of the triangle formed by that point and its two immediate neighbours. A point with a tiny triangle barely affects the shape, so it is the safest to remove.
The algorithm works iteratively. It finds the live point with the smallest effective area, removes it, relinks its neighbours, and recomputes the effective areas of those two neighbours (because their triangles changed). It repeats until the geometry has been reduced to the target number of points you chose with the slider. Endpoints of an open line, and enough points to keep a closed ring valid, are always retained.
The tool walks the GeoJSON structure recursively, applying this to every LineString, MultiLineString, Polygon and MultiPolygon it finds, whether they sit in a single Feature or a whole FeatureCollection. It then reports the total vertex count before and after, plus the change in byte size.
Tips and notes
- Keeping
30%of vertices is a good starting point for web maps; drop lower for thumbnails, higher for detailed views. - Triangle area is computed in coordinate units, so the same setting behaves consistently across a dataset.
- Polygon rings are kept at four or more points so each shape stays closed and valid.
Everything runs locally in your browser — your GeoJSON is never uploaded.