Exporting GeoJSON

Geoman provides several methods to export features as GeoJSON. You can export all features, features from specific sources, or filtered features based on shape types.

Basic Export Methods

Export All Features

The simplest way to export all features is using exportGeoJson():

const allFeatures = gm.features.exportGeoJson();

This returns a GeoJSON FeatureCollection containing all features from Geoman's internal state. This method provides the latest feature data, even during event handlers before MapLibre has committed changes.

Export from MapLibre Source

If you need to export features directly from MapLibre's source (which may lag slightly behind during rapid updates or in event handlers), use exportGeoJsonFromSource():

const featuresFromSource = gm.features.exportGeoJsonFromSource();

Export with Options

Both export methods support filtering by shape types and customizing the ID property name:

// Export only polygons and circles
const polygonsAndCircles = gm.features.exportGeoJson({
  allowedShapes: ['polygon', 'circle']
});

// Use a custom property name for feature IDs
const withCustomId = gm.features.exportGeoJson({
  idPropertyName: 'featureId'
});

// Combine options
const filtered = gm.features.exportGeoJsonFromSource({
  allowedShapes: ['marker', 'line'],
  idPropertyName: 'customId'
});

Exported GeoJSON Structure

The exported GeoJSON follows this structure:

interface GeoJsonShapeFeatureCollection {
  type: 'FeatureCollection';
  features: Array<{
    type: 'Feature';
    geometry: {
      type: string;
      coordinates: any[];
    };
    properties: {
      __gm_id?: FeatureId;
      shape: FeatureShape;
      center?: LngLat;
      text?: string;
    };
  }>;
}

Complete Example

Here's a complete example showing different export methods:

const gm = new Geoman(map);

// Draw some features...

// Export all features
const allFeatures = gm.features.exportGeoJson();
console.log('All features:', allFeatures);

// Save to file
function downloadGeoJson(geojson: GeoJsonShapeFeatureCollection, filename: string) {
  const blob = new Blob([JSON.stringify(geojson)], { type: 'application/json' });
  const url = URL.createObjectURL(blob);
  const link = document.createElement('a');
  link.href = url;
  link.download = filename;
  document.body.appendChild(link);
  link.click();
  document.body.removeChild(link);
  URL.revokeObjectURL(url);
}

// Download different exports
downloadGeoJson(allFeatures, 'all-features.geojson');