GeoJason

GeoJSON Simplifier

Simplify complex GeoJSON geometries to reduce file size while preserving shape accuracy.

0.01

How GeoJSON Simplification Works

This tool uses the Douglas-Peucker algorithm (also known as the Ramer-Douglas-Peucker algorithm) to reduce the number of vertices in GeoJSON geometries while preserving the overall shape. The algorithm works by recursively finding the point farthest from a line segment between two endpoints. If that distance is below the tolerance threshold, all intermediate points are removed. If it exceeds the threshold, the farthest point is kept and the process recurses on both sub-segments.

Simplification is applied to LineString and Polygon geometries. Point features pass through unchanged since they have no vertices to remove. The tool uses the "high quality" variant of the algorithm, which processes each ring and segment independently for better shape preservation.

Choosing the Right Tolerance

The tolerance value represents the maximum distance (in degrees) that a simplified edge can deviate from the original geometry. As a rough guide:

  • 0.001 — minimal simplification, good for city-level detail. A polygon with 10,000 vertices might reduce to 5,000.
  • 0.01 — moderate simplification, suitable for country-level maps. File sizes typically shrink by 50-70%.
  • 0.05–0.1 — aggressive simplification, best for world-overview maps. Complex coastlines become smooth curves.

Watch the map preview as you adjust the slider to find the right balance between file size and visual fidelity for your use case. The percentage reduction is shown in the status bar after each adjustment.

When to Simplify GeoJSON

  • Reducing file size for faster loading in web mapping applications
  • Improving rendering performance on mobile devices
  • Creating overview tiles or thumbnails from detailed boundary data
  • Preparing data for APIs with payload size limits
  • Building zoom-dependent layers where lower zoom levels use simpler geometry

Simplification Pitfalls

Over-simplification can introduce geometry errors. Watch for these common issues:

  • Self-intersecting polygons — aggressive simplification can cause polygon edges to cross each other, creating invalid geometry
  • Topology breaks — adjacent polygons that shared a boundary before simplification may develop gaps or overlaps afterward, since each polygon is simplified independently
  • Small feature loss — very small islands, enclaves, or narrow peninsulas may collapse to zero area and disappear entirely

After simplifying, validate the result with the validator and visually check the map for artifacts. For topology-preserving simplification, consider using TopoJSON, which simplifies shared boundaries together.

Programmatic Equivalent

In JavaScript with Turf.js:

JavaScriptconst simplified = turf.simplify(featureCollection, {
  tolerance: 0.01,
  highQuality: true
});

For additional file size reduction, combine simplification with precision reduction or minification. For a comprehensive approach, see the file size optimization guide.