turf.segmentReduce

What is turf.segmentReduce?

turf.segmentReduce folds every two-vertex segment in a GeoJSON object into one accumulator, with the segment yielded as a LineString Feature.

turf.segmentReduce(geojson, callback, initialValue?) → any

The callback receives (previousValue, currentSegment, featureIndex, multiFeatureIndex, geometryIndex, segmentIndex).

When would you use turf.segmentReduce?

Use turf.segmentReduce for per-edge accumulations — total network length (identical to turf.length when summed with unit care), counts of steep edges, or maps from edge id to bearing.

It avoids materialising all segments into a flat array (as a manual flattenEach + loop would), which keeps memory flat even on very large road networks.

1const totalLength = turf.segmentReduce(
2  network,
3  (sum, seg) => sum + turf.length(seg, { units: 'meters' }),
4  0
5);

FAQs

How do I install Turf.js to use this function?

Install npm install @turf/meta and import import { segmentReduce } from '@turf/meta', or use turf.segmentReduce via the umbrella @turf/turf.

Are the segments Features or raw arrays?

Each is a two-vertex LineString Feature — so you can pass it directly to turf.length, turf.bearing, or any line-accepting function.

Does segmentReduce process polygon rings?

Yes. Outer and inner rings contribute their edges too. If you want only line geometries, filter your input first.

When should I use segmentReduce vs length?

turf.length computes the length of a single line in one call. segmentReduce is the right tool when your accumulation is not a plain length — for example counting segments, bucketing by bearing, or returning a non-scalar result.