toJson method
Converts the GeoJsonFeatureProperties to a Map with keys 'groupIndex', 'value' and 'center'.
Implementation
Map<String, dynamic> toJson() => {
'group_index': groupIndex,
'value': value,
'center': center == null
? null
: <double>[center!.longitude, center!.latitude],
'osm_id': osmId,
'osm_type': osmType,
'distance': distance,
'category_ids': categoryIds,
'osm_tags': osmTags,
}..removeWhere((key, value) => value == null);