turf.truncate

What is turf.truncate?

turf.truncate walks every coordinate in a GeoJSON Feature, FeatureCollection, or Geometry and trims it to a given decimal precision. Optionally it also strips the Z value.

turf.truncate(geojson, options?) → Feature<Geometry>

Options include:

• precision — number of decimal places (default 6)
• coordinates — maximum coordinates per position, e.g. 2 to strip Z (default 3)
• mutate — boolean (default false); when true, mutates the input in place

When would you use turf.truncate?

Use turf.truncate to shrink GeoJSON payloads before sending to a client or saving to storage. Six decimal places of longitude/latitude ≈ 11 cm on the ground, which is more than enough for almost every map interaction — trimming to six is a lossless change for UI purposes but can cut file size substantially for dense geometries.

In Node.js ETL, turf.truncate is a common step before emitting static GeoJSON assets served by Gatsby, Netlify, or Vercel. It also keeps Git diffs stable when you check GeoJSON fixtures into a repo and want cosmetic edits to remain small.

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FAQs

How much precision do I need?

6 decimal places ≈ 11 cm — safe for almost all mapping work. 5 ≈ 1.1 m (fine for address-level work). 4 ≈ 11 m (good for city-block scale). 3 ≈ 110 m (noticeable drift in urban mapping). Start with 6 and reduce only when payload size is critical.

Does it change the shape?

Rounding coordinates shifts them slightly. At precision 6 the shift is sub-decimetre and imperceptible. At lower precision the changes become visible, especially for dense polygons.

How do I install just truncate?

npm install @turf/truncate. It depends on @turf/meta and @turf/helpers.

Can I strip Z values?

Yes — set coordinates: 2 to keep only [lng, lat] in every position and drop any altitude or M value.