GeoJSON Support

This document covers Leaflet's comprehensive GeoJSON support system, which enables parsing, displaying, and converting geographic data in the GeoJSON format. The system provides both input capabilities (loading GeoJSON data onto maps) and output capabilities (converting Leaflet layers back to GeoJSON format).

For information about vector layer rendering and styling, see Vector Layers. For marker-specific functionality, see Markers and Icons.

Architecture Overview

Leaflet's GeoJSON support is built around a central GeoJSON class that extends FeatureGroup, along with static utility functions for coordinate transformations and geometry conversions. The system also extends core layer types with toGeoJSON() methods to enable round-trip conversions.

100%

Architecture: GeoJSON Support System

GeoJSON Class

The GeoJSON class serves as the primary interface for working with GeoJSON data in Leaflet. It extends FeatureGroup to provide layer management capabilities while adding GeoJSON-specific functionality.

Constructor and Options

The GeoJSON class accepts optional GeoJSON data and configuration options:

Option	Type	Default	Description
pointToLayer	Function	Creates Marker	Converts GeoJSON points to Leaflet layers
style	Function	{}	Styling function for vector layers
onEachFeature	Function	No-op	Callback executed for each feature
filter	Function	true	Feature filtering function
coordsToLatLng	Function	coordsToLatLng	Coordinate transformation function
markersInheritOptions	Boolean	false	Whether markers inherit group options

100%

GeoJSON Class Initialization and Options

Core Methods

addData(geojson)

The addData() method processes GeoJSON data and converts it to appropriate Leaflet layers:

100%

addData Method Processing Flow

resetStyle(layer) and setStyle(style)

Style management methods allow dynamic styling updates:

• resetStyle() - Resets layer styles to original GeoJSON styles
• setStyle() - Applies new styling functions to all layers

Static Utility Functions

Geometry Conversion

geometryToLayer(geojson, options)

Converts GeoJSON geometries to appropriate Leaflet layer types:

GeoJSON Type	Leaflet Layer	Notes
Point	Marker	Uses pointToLayer option if provided
MultiPoint	FeatureGroup	Contains multiple markers
LineString	Polyline	Single line
MultiLineString	Polyline	Multi-dimensional coordinates
Polygon	Polygon	Single polygon with optional holes
MultiPolygon	Polygon	Multi-dimensional coordinates
GeometryCollection	FeatureGroup	Recursive geometry processing
FeatureCollection	FeatureGroup	Recursive feature processing

100%

geometryToLayer Conversion Logic

Coordinate Transformations

coordsToLatLng(coords) and coordsToLatLngs(coords, levelsDeep, coordsToLatLng)

Handle coordinate system conversions between GeoJSON format ([lng, lat, alt]) and Leaflet format (LatLng(lat, lng, alt)):

100%

Coordinate System Transformations

Layer toGeoJSON Extensions

Leaflet extends core layer types with toGeoJSON() methods to enable converting layers back to GeoJSON format.

Point-based Layers

Point-based layers (Marker, Circle, CircleMarker) share a common PointToGeoJSON mixin:

100%

Point Layer GeoJSON Conversion

Vector Layers

Polyline toGeoJSON

Polylines convert to LineString or MultiLineString based on coordinate structure:

100%

Polyline GeoJSON Conversion

Polygon toGeoJSON

Polygons handle both simple polygons and multi-polygons with holes:

100%

Polygon GeoJSON Conversion

LayerGroup Collections

LayerGroup handles collections and produces FeatureCollection, GeometryCollection, or MultiPoint output:

100%

LayerGroup GeoJSON Conversion

Feature Normalization

The asFeature() and getFeature() functions ensure consistent GeoJSON Feature format:

Input Type	Output
Feature	Returns as-is
FeatureCollection	Returns as-is
Geometry object	Wraps in Feature with empty properties

Usage Patterns

Basic GeoJSON Loading

new GeoJSON(geojsonData, {
    style: function (feature) {
        return {color: feature.properties.color};
    },
    onEachFeature: function (feature, layer) {
        layer.bindPopup(feature.properties.description);
    }
}).addTo(map);

Custom Point Rendering

new GeoJSON(geojsonData, {
    pointToLayer: function (feature, latlng) {
        return new CircleMarker(latlng, {radius: feature.properties.size});
    }
});

Round-trip Conversion

// Layer to GeoJSON
const geojson = layerGroup.toGeoJSON();

// GeoJSON back to layers
const layers = new GeoJSON(geojson);