osmtogeojson

Converts OpenStreetMap data (OSM XML or Overpass API JSON) to GeoJSON FeatureCollections. A pure Dart port of the osmtogeojson npm library.

Installation

dart pub add osmtogeojson

Usage

import 'package:osmtogeojson/osmtogeojson.dart';

// From an Overpass API JSON response:
final json = {
  'elements': [
    {'type': 'node', 'id': 1, 'lat': 48.2082, 'lon': 16.3738,
     'tags': {'name': 'Vienna'}},
  ],
};

// Full FeatureCollection:
final collection = osmToGeoJson(json);
print(collection['type']); // "FeatureCollection"

// Or iterate features individually:
for (final feature in osmToGeoJsonFeatures(json)) {
  print(feature['id']);         // "node/1"
  print(feature['geometry']);   // {type: Point, coordinates: [16.3738, 48.2082]}
  print(feature['properties']); // {id: "node/1", name: "Vienna"}
}

OSM XML input is auto-detected — pass a String instead of a Map:

const xml = '''
  <osm>
    <node id="1" lat="48.2082" lon="16.3738">
      <tag k="name" v="Vienna" />
    </node>
  </osm>
''';
final collection = osmToGeoJson(xml);

Options

The optional OsmToGeoJsonOptions object supports:

  • flatProperties (default true) — if true, each feature's properties will be a simple key-value list instead of a structured object with separate tags and meta.
  • uninterestingTags (default {source, source_ref, …}) — tag keys to ignore when deciding whether a node should be a standalone POI.
  • polygonFeatures — tag patterns that cause a closed way to be treated as a Polygon rather than LineString. Defaults to a built-in set based on OSM conventions.
  • deduplicator — custom function (a, b) => merged for resolving duplicate OSM elements. Defaults to preferring the higher version.
  • verbose (default false) — when true, prints warnings for ignored or tainted features.

Supported features

  • All major OSM geometries — Point, LineString, Polygon, MultiPolygon, MultiLineString.
  • Relations — multipolygon (simple & complex), boundary, route, waterway.
  • Overpass output modes — out center, out bounds, out geom.
  • Deduplication — duplicate elements merged; custom deduplicator supported.
  • Tainting — incomplete features emitted with tainted: true instead of being silently dropped.
  • Polygon winding — corrected to GeoJSON right-hand rule.

Libraries

osmtogeojson
Converts OpenStreetMap data to GeoJSON.