GeoJSON is becoming a very popular data format among many GIS technologies and services — it's simple, lightweight, straightforward, and Leaflet is quite good at handling it. In this example, you'll learn how to create and interact with map vectors created from GeoJSON objects.
View example on a separate page →
According to http://geojson.org:
GeoJSON is a format for encoding a variety of geographic data structures. A GeoJSON object may represent a geometry, a feature, or a collection of features. GeoJSON supports the following geometry types: Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, and GeometryCollection. Features in GeoJSON contain a geometry object and additional properties, and a feature collection represents a list of features.
Leaflet supports all of the GeoJSON types above, but Features and FeatureCollections work best as they allow you to describe features with a set of properties. We can even use these properties to style our Leaflet vectors. Here's an example of a simple GeoJSON feature:
var geojsonFeature = {
"type": "Feature",
"properties": {
"name": "Coors Field",
"amenity": "Baseball Stadium",
"popupContent": "This is where the Rockies play!"
},
"geometry": {
"type": "Point",
"coordinates": [-104.99404, 39.75621]
}
};
GeoJSON objects are added to the map through a GeoJSON layer. To create it and add it to a map, we can use the following code:
L.geoJson(geojsonFeature).addTo(map);
GeoJSON objects may also be passed as an array of valid GeoJSON objects.
var myLines = [{
"type": "LineString",
"coordinates": [[-100, 40], [-105, 45], [-110, 55]]
}, {
"type": "LineString",
"coordinates": [[-105, 40], [-110, 45], [-115, 55]]
}];
Alternatively, we could create an empty GeoJSON layer and assign it to a variable so that we can add more features to it later.
var myLayer = L.geoJson().addTo(map);
myLayer.addData(geojsonFeature);
The style
option can be used to style features two different ways. First, we can pass a simple object that styles all paths (polylines and polygons) the same way:
var myLines = [{
"type": "LineString",
"coordinates": [[-100, 40], [-105, 45], [-110, 55]]
}, {
"type": "LineString",
"coordinates": [[-105, 40], [-110, 45], [-115, 55]]
}];
var myStyle = {
"color": "#ff7800",
"weight": 5,
"opacity": 0.65
};
L.geoJson(myLines, {
style: myStyle
}).addTo(map);
Alternatively, we can pass a function that styles individual features based on their properties. In the example below we check the "party" property and style our polygons accordingly:
var states = [{
"type": "Feature",
"properties": {"party": "Republican"},
"geometry": {
"type": "Polygon",
"coordinates": [[
[-104.05, 48.99],
[-97.22, 48.98],
[-96.58, 45.94],
[-104.03, 45.94],
[-104.05, 48.99]
]]
}
}, {
"type": "Feature",
"properties": {"party": "Democrat"},
"geometry": {
"type": "Polygon",
"coordinates": [[
[-109.05, 41.00],
[-102.06, 40.99],
[-102.03, 36.99],
[-109.04, 36.99],
[-109.05, 41.00]
]]
}
}];
L.geoJson(states, {
style: function(feature) {
switch (feature.properties.party) {
case 'Republican': return {color: "#ff0000"};
case 'Democrat': return {color: "#0000ff"};
}
}
}).addTo(map);
Points are handled differently than polylines and polygons. By default simple markers are drawn for GeoJSON Points. We can alter this by passing a pointToLayer
function in a GeoJSON options object when creating the GeoJSON layer. This function is passed a LatLng and should return an instance of ILayer, in this case likely a Marker or CircleMarker.
Here we're using the pointToLayer
option to create a CircleMarker:
var geojsonMarkerOptions = {
radius: 8,
fillColor: "#ff7800",
color: "#000",
weight: 1,
opacity: 1,
fillOpacity: 0.8
};
L.geoJson(someGeojsonFeature, {
pointToLayer: function (feature, latlng) {
return L.circleMarker(latlng, geojsonMarkerOptions);
}
}).addTo(map);
We could also set the style
property in this example — Leaflet is smart enough to apply styles to GeoJSON points if you create a vector layer like circle inside the pointToLayer
function.
The onEachFeature
option is a function that gets called on each feature before adding it to a GeoJSON layer. A common reason to use this option is to attach a popup to features when they are clicked.
function onEachFeature(feature, layer) {
// does this feature have a property named popupContent?
if (feature.properties && feature.properties.popupContent) {
layer.bindPopup(feature.properties.popupContent);
}
}
var geojsonFeature = {
"type": "Feature",
"properties": {
"name": "Coors Field",
"amenity": "Baseball Stadium",
"popupContent": "This is where the Rockies play!"
},
"geometry": {
"type": "Point",
"coordinates": [-104.99404, 39.75621]
}
};
L.geoJson(geojsonFeature, {
onEachFeature: onEachFeature
}).addTo(map);
The filter
option can be used to control the visibility of GeoJSON features. To accomplish this we pass a function as the filter
option. This function gets called for each feature in your GeoJSON layer, and gets passed the feature
and the layer
. You can then utilise the values in the feature's properties to control the visibility by returning true
or false
.
In the example below "Busch Field" will not be shown on the map.
var someFeatures = [{
"type": "Feature",
"properties": {
"name": "Coors Field",
"show_on_map": true
},
"geometry": {
"type": "Point",
"coordinates": [-104.99404, 39.75621]
}
}, {
"type": "Feature",
"properties": {
"name": "Busch Field",
"show_on_map": false
},
"geometry": {
"type": "Point",
"coordinates": [-104.98404, 39.74621]
}
}];
L.geoJson(someFeatures, {
filter: function(feature, layer) {
return feature.properties.show_on_map;
}
}).addTo(map);
View the example page to see in detail what is possible with the GeoJSON layer.