Folium

Folium is a Python library used for visualizing geospatial data interactively on web maps. Leveraging the capabilities of Leaflet.js, Folium allows users to create maps directly within Python code, making it an accessible and powerful tool for geospatial visualization and analysis.

With Folium, users can create various types of interactive maps, including point maps, choropleth maps, heatmaps, and vector overlays, by simply specifying geographic coordinates and map styling options. The library provides intuitive APIs for customizing map features such as markers, popups, tooltips, legends, and map layers, enabling users to create visually appealing and informative maps with ease.

Folium integrates with other popular Python libraries such as Pandas and Matplotlib, allowing users to visualize geospatial data stored in DataFrame objects or plot data directly onto Folium maps. It also supports various tile providers and basemaps, enabling users to choose from a wide range of map styles and sources.

Creating Interactive Maps in Folium

Creating maps with folium is straightforward. We simply pass the latitude and longitude of the point of interest (POI) and specify a zoom level. We can then drop a marker on the point of interest, and interact with the map however we’d like.

We can get the latitude and longitude for a given POI by performing a google search. Latitude ranges from -90 to 90 degrees, longitude from -180 to 180 degrees. The latitude and longitude for the DMACC Ankeny campus is (41.5996, -93.6276), which is (latitude, longitude). Note that for US coordinates, the longitude will always be negative. An illustration is provided below:

To illustrate, let’s render a map over the park I used to play at as a child (Durkin Park on the southwest side of Chicago). Note that zoom level provides more detail as the number gets larger. A zoom level of 4 would show the entire US; a zoom level of 17 would render roughly a city block:

import folium

# Latitude and longitude for Durkin Park, 84th & Kolin Ave, Chicago IL. 
lat = 41.739
lon = -87.729
zoom = 18

m = folium.Map(location=[lat, lon], zoom_start=zoom)
folium.Marker(location=[lat, lon]).add_to(m)

m

A few things to note about the code used to render the map:

• We start by importing the folium library.
• The lat/lon for Durkin Park was obtained by a simple google search.
• I used a level 18 zoom but this is not necessary since the map is dynamic and can be resized.
• To add the marker to the map, we call .add_to(m).
• We included m by itself in the last line of the cell in order for the map to render. Without doing this, the map would not display.

We can change the color of the marker by passing an additional argument into folium.Marker. I’ll place a second marker in another park I used to visit when I was younger, Scottsdale Park. I’ll make this second marker red.

# Durkin Park coordinates.
lat0 = 41.739
lon0 = -87.729

# Scottsdale Park coordinates. 
lat1 = 41.7416
lon1 = -87.7356

# Center map at midway point between parks.
mid_lat = (lat0 + lat1) / 2
mid_lon = (lon0 + lon1) / 2

# Specify zoom level. 
zoom = 16

# Initialize map.
m = folium.Map(location=[mid_lat, mid_lon], zoom_start=zoom)

# Add Durkin Park marker.
folium.Marker(
    location=[lat0, lon0],
    popup="Durkin Park",
    ).add_to(m)

# Add Scottsdale Park marker.
folium.Marker(
    location=[lat1, lon1],
    popup="Scottsdale Park",
    icon=folium.Icon(color="red")
    ).add_to(m)

m

One final point: We can replace the standard markers with circle markers by using folium.CircleMarker. radius controls the size of the markers and color/fill_color set the color of the marker:

m = folium.Map(location=[mid_lat, mid_lon], zoom_start=zoom)

# Add Durkin Park circle marker.
folium.CircleMarker(
    location=[lat0, lon0], 
    radius=7, 
    popup="Durkin Park",
    color="red", 
    fill_color="red", 
    fill=True,
    fill_opacity=1
    ).add_to(m)

# Add Scottsdale Park marker.
folium.CircleMarker(
    location=[lat1, lon1], 
    radius=7, 
    popup="Scottsdale Park",
    color="red", 
    fill_color="red", 
    fill=True,
    fill_opacity=1
    ).add_to(m)


# Connect parks with green line. 
points = [(lat0, lon0), (lat1, lon1)]
folium.PolyLine(points, color="green").add_to(m)

m