Convert GeoJSON to TopoJSON locally - shared-arc topology, much smaller for web maps. No upload.
Running locally on your device ...
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Your files never left your device
No. Everything runs in your browser - your file never leaves your device. How this is verifiable
TopoJSON is an extension of GeoJSON that stores topology: instead of repeating shared boundaries between neighbouring shapes, it records each boundary once as an arc and references it. For maps of regions, countries or districts that share borders, this makes the file dramatically smaller - which is why D3 and many web-map pipelines prefer it. This tool reads your GeoJSON and builds a TopoJSON topology.
The conversion detects shared arcs across all features and quantizes the coordinates onto a grid, the two techniques that give TopoJSON its small size. Feature properties are preserved. The result is a single TopoJSON object you can load into D3, feed to mapshaper or ship to a browser as a compact basemap.
Everything runs entirely locally in the browser - your possibly sensitive location data never leaves your device. Honestly framed: quantization rounds coordinates slightly, so a round-trip back to GeoJSON is exact only within that grid tolerance (irrelevant at normal map zoom). An invalid or empty GeoJSON is rejected with a clear message.
| Input formats | GEOJSON, JSON |
|---|---|
| Output format | TOPOJSON |
| Batch processing | No |
| Processing | Locally in your browser (JavaScript) |
| File upload | None |
Limitations: Converts GeoJSON to TopoJSON: a topology with shared arcs and quantized coordinates, often far smaller than the GeoJSON. Coordinates WGS84. Quantization rounds coordinates slightly (lossy at high zoom); round-trips with TopoJSON to GeoJSON within that tolerance. An invalid or empty GeoJSON is rejected with a clear error.
It stores each shared boundary once as an arc and references it, instead of repeating it on every neighbouring shape, and quantizes coordinates onto a grid.
Yes, feature properties are carried into the TopoJSON objects.
Geometry is preserved up to the quantization grid; coordinates are rounded slightly, which is irrelevant at normal map zoom. Round-trips with TopoJSON to GeoJSON within that tolerance.
No, the conversion happens entirely locally in the browser; location data never leaves your device.