geojson_advanced_on_each_feature.md

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import folium

Advanced GeoJSON Customization with on_each_feature

The on_each_feature parameter in folium.GeoJson provides powerful customization capabilities by allowing you to execute JavaScript code for each feature in your GeoJSON data. This is particularly useful for:

• Custom tooltip and popup handling for complex geometries like MultiPoint

• Adding custom event listeners

• Implementing advanced styling logic

• Working with geometry types that need special handling

Understanding on_each_feature

The on_each_feature parameter accepts a folium.utilities.JsCode object containing JavaScript code that will be executed for each feature. The JavaScript function receives two parameters:

• feature: The GeoJSON feature object

• layer: The Leaflet layer object representing the feature

Basic Example

import folium
from folium.utilities import JsCode
import json

# Simple point data
geojson_data = {
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "properties": {"name": "Location 1", "value": 100},
            "geometry": {"type": "Point", "coordinates": [77.5946, 12.9716]}  # Central Bangalore
        },
        {
            "type": "Feature",
            "properties": {"name": "Location 2", "value": 200},
            "geometry": {"type": "Point", "coordinates": [77.6200, 12.9800]}  # Northeast Bangalore
        }
    ]
}

# Custom JavaScript to add popups
on_each_feature = JsCode("""
function(feature, layer) {
    layer.bindTooltip(
        '<b>' + feature.properties.name + '</b><br>' +
        'Value: ' + feature.properties.value
    );

    layer.bindPopup(
        '<b>' + ' This is popup ' + '</b><br>' +
        '<b>' + feature.properties.name + '</b><br>' +
        'Value: ' + feature.properties.value
    );
}
""")

m = folium.Map(location=[12.9716, 77.5946], zoom_start=10)

folium.GeoJson(
    geojson_data,
    on_each_feature=on_each_feature
).add_to(m)

m

The on_each_feature parameter provides the flexibility needed to handle complex GeoJSON scenarios that the standard tooltip and popup classes cannot address, particularly for MultiPoint geometries and advanced interactive features.

References

• Leaflet GeoJSON Tutorial - Comprehensive guide to using GeoJSON with Leaflet, including the onEachFeature option that inspired folium's on_each_feature parameter.