Folium

11. Folium#

Open In Colab

11.1. Introduction#

Folium is a powerful Python library that enables the creation of interactive maps using Leaflet.js. It provides a simple interface to visualize geospatial data and integrates well with Pandas, GeoPandas, and other geospatial libraries.

11.1.1. Learning Objectives#

By the end of this lecture, you will:

  • Understand what Folium is and how it works.

  • Learn to create basic maps and add markers.

  • Explore how to visualize geospatial data.

  • Customize maps with different layers and styles.

11.2. 1. Installing and Importing Folium#

To install Folium, run the following command:

pip install folium

Then, import Folium in Python:

import folium

11.3. 2. Creating a Basic Map#

A Folium map is centered on a specific latitude and longitude.

m = folium.Map(location=[37.7749, -122.4194], zoom_start=10)
m.save("map.html")  # Save map as an HTML file
m  # Display the map in Jupyter Notebook

11.3.1. Map Parameters#

  • location: Center of the map (latitude, longitude).

  • zoom_start: Initial zoom level.

  • tiles: The map style (default: "OpenStreetMap").

11.4. 3. Adding Markers and Popups#

Folium allows adding markers to highlight specific locations.

m = folium.Map(location=[37.7749, -122.4194], zoom_start=10)
folium.Marker(
    [37.7749, -122.4194],
    popup="San Francisco",
    tooltip="Click for info",
    icon=folium.Icon(color="blue", icon="info-sign"),
).add_to(m)

m.save("map_with_marker.html")
m

11.5. 4. Adding GeoJSON and Choropleth Layers#

Folium supports GeoJSON and Choropleth layers for visualizing geographic data.

11.5.1. Adding a GeoJSON Layer#

import json

geojson_data = {
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "geometry": {"type": "Point", "coordinates": [-122.4194, 37.7749]},
            "properties": {"name": "San Francisco"},
        }
    ],
}

m = folium.Map(location=[37.7749, -122.4194], zoom_start=10)
folium.GeoJson(geojson_data, name="GeoJSON Layer").add_to(m)
m

11.5.2. Creating a Choropleth Map#

import pandas as pd

# Sample data: FIPS codes and values
data = pd.DataFrame(
    {"FIPS": ["06075"], "Value": [100]}  # San Francisco county FIPS code
)

m = folium.Map(location=[37.7749, -122.4194], zoom_start=6)
folium.Choropleth(
    geo_data="https://raw.githubusercontent.com/PublicaMundi/MappingAPI/master/data/geojson/us-states.json",
    data=data,
    columns=["FIPS", "Value"],
    key_on="feature.id",
    fill_color="YlGn",
    fill_opacity=0.7,
    line_opacity=0.2,
    legend_name="Sample Data",
).add_to(m)

m

11.6. 5. Customizing Map Tiles#

Folium allows switching between different map tiles:

m = folium.Map(location=[37.7749, -122.4194], zoom_start=10)
m

Other tile options:

  • CartoDB positron

  • CartoDB dark_matter

11.7. 6. Adding Layer Controls#

To allow toggling between layers:

m = folium.Map(location=[37.7749, -122.4194], zoom_start=10)
folium.TileLayer("CartoDB positron").add_to(m)
folium.TileLayer("CartoDB darkmatter").add_to(m)
folium.LayerControl().add_to(m)
m

11.8. 7. Saving and Sharing Maps#

Folium maps can be saved as HTML files:

m.save("interactive_map.html")

11.9. Summary#

  • Folium is a Python library for creating interactive maps.

  • Basic maps can be customized with markers, popups, and tooltips.

  • Advanced features include GeoJSON, choropleth maps, and tile layers.

  • Maps can be saved as HTML files and shared easily.

11.10. Further Reading#

Contents